PHYSICS MCQ'S 1

1. The SI standard of time is based on: 

A. the daily rotation of the earth 
B. the frequency of light emitted by Kr86 
C. the yearly revolution of the earth about the sun 
D. a precision pendulum clock 
E. none of these 
Ans: E 

2. A nanosecond is:

 A. 109 s 
B. 10−9 s 
C. 10−10 s 
D. 10−10 s 
E. 10−12 
Ans: B 

3. The SI standard of length is based on: 

A. the distance from the north pole to the equator along a meridian passing through Paris 
B. wavelength of light emitted by Hg198 
C. wavelength of light emitted by Kr86 
D. a precision meter stick in Paris E. the speed of light 
Ans: E 

4. In 1866, the U. S. Congress defined the U. S. yard as exactly 3600/3937 international meter. This was done primarily because: 

A. length can be measured more accurately in meters than in yards 
B. the meter is more stable than the yard 
C. this definition relates the common U. S. length units to a more widely used system 
D. there are more wavelengths in a yard than in a meter 
E. the members of this Congress were exceptionally intelligent 
Ans: C 

5. Which of the following is closest to a yard in length? 

A. 0.01 m 
B. 0.1 m 
C. 1 m 
D. 100 m 
E. 1000 m 
Ans: C

6. There is no SI base unit for area because: 

A. an area has no thickness; hence no physical standard can be built
 B. we live in a three (not a two) dimensional world 
C. it is impossible to express square feet in terms of meters 
D. area can be expressed in terms of square meters E. area is not an important physical quantity 
Ans: D 

7. The SI base unit for mass is: 

A. gram 
B. pound 
C. kilogram 
D. ounce 
E. kilopound 
Ans: C 

8. A gram is: 

A. 10−6 kg 
B. 10−3 kg
C. 1 kg 
D. 103 kg 
E. 106 kg
 Ans: B 

9. Which of the following weighs about a pound? 

A. 0.05 kg 
B. 0.5 kg 
C. 5 kg 
D. 50 kg 
E. 500 kg 
Ans: D 

10. (5.0 × 104) × (3.0 × 106) = 

A. 1.5 × 10^9 
B. 1.5 × 10^10 
C. 1.5 × 10^11 
D. 1.5 × 10^12 
E. 1.5 × 10^13 
Ans: C

BRONSTED-LOWRY THEORY OF ACIDS AND BASIS

A more satisfactory theory was proposed in 1923 by the Danish chemist Johannes Brønsted and independently by Thomas Lowry, a British chemist. Their theory states that an acid is a proton (hydrogen ion, H⁺) donor and a base a proton acceptor. Although the acid must still contain hydrogen, the Brønsted-Lowry theory does not require an aqueous medium. For example, liquid ammonia, which acts as a base in aqueous solution, can act as an acid in the absence of water by transferring a proton to a base and forming the amide anion (negative ion) NH₂^-: NH₃ + base⇄NH₂^- + base + H⁺The Brønsted-Lowry definition of acids and bases also explains why a strong acid displaces a weak acid from its compounds (and likewise for strong and weak bases). Here acid-base reactions are viewed as a competition for protons. In terms of a general chemical equation, the reaction of Acid (1) with Base (2) Acid (1) + Base (2)⇄Acid (2) + Base (1)results in the transfer of a proton from Acid (1) to Base (2). In losing the proton, Acid (1) becomes its conjugate base, Base (1). In gaining a proton, Base (2) becomes its conjugate acid, Acid (2). The equilibrium represented by the equation above may be displaced either to the left or to the right, and the actual reaction will take place in the direction that produces the weaker acid-base pair. For example, hydrogen chloride (HCl) is a strong acid in water because it readily transfers a proton to water to form a hydronium ion: HCl + H₂O⇄H₃O⁺ + Cl^-The equilibrium lies mostly to the right because the conjugate base of HCl, Cl^-, is a weak base, and H₃O⁺, the conjugate acid of H₂O, is a weak acid.
In contrast, hydrogen fluoride, HF, is a weak acid in water because it does not readily transfer a proton to water: HF + H₂O⇄H₃O⁺ + F^-This equilibrium lies mostly to the left because H₂O is a weaker base than F^-, and because HF is a weaker acid (in water) than H₃O⁺. The Brønsted-Lowry theory also explains why water can be amphoteric, that is, why it can serve as either an acid or a base. Water serves as a base in the presence of an acid that is stronger than water (such as HCl), in other words, an acid that has a greater tendency to dissociate than does water: HCl + H₂O⇄H₃O⁺ + Cl^-Water can also serve as an acid in the presence of a base that is stronger than water (such as ammonia): NH₃ + H₂O⇄NH₄⁺ + OH^-

REAL GASES AND IDEAL GASES

A gas that obeyed the ideal gas equation exactly under any conditions would be an ideal gas, but no actual gas perfectly conforms to the equation at all temperatures and pressures. Under the conditions of high temperatures and low pressures present over much of Earth’s surface, however, most real gases behave as ideal gases. Gases with boiling points below –173ºC (-279ºF), such as hydrogen, oxygen, nitrogen, and the noble gases, come closest to being ideal gases. Gases with relatively high boiling points, such as carbon dioxide, obey the gas laws only approximately.

IDEAL GAS EQUATION

The gas laws can be combined as a more general expression called the ideal gas equation or ideal gas law: PV = nRTIn this equation, n represents the number of moles of a gas. The constant R on the right-hand side of the equation is a universal constant and has a value of 8.31447 J/mol·K. This single equation can predict the behavior of a gas even if multiple conditions are changed simultaneously. If both the pressure and volume of a gas double, for example, its temperature will increase by a factor of four.

AVOGADRO'S LAW

The behavior of gases described by Boyle’s, Charles’s, and Dalton’s laws is nearly the same for all gases. Avogadro’s law states that under identical conditions of temperature and pressure, equal volumes of different gases contain equal numbers of particles (atoms or molecules).
The temperature 0ºC (32ºF) and the pressure equal to the pressure Earth’s atmosphere exerts at sea level are called standard temperature and pressure (STP). According to Avogadro’s law, 1 cubic meter of oxygen at STP contains the same number of particles as 1 cubic meter of nitrogen at STP. Restated, Avogadro's law says that one mole of any gas at STP occupies a volume of 22.4 liters. A mole is 6.02 × 10²³ basic particles (atoms or molecules) of a substance. The extremely large number 6.02 × 10²³ is called Avogadro's number.

DALTON'S LAW

Dalton’s law states that in a mixture of different gases, such as air, the sum of the partial pressures of all the gases equals the total pressure. The partial pressure of a gas is the pressure that gas would exert if it was the only gas present. This law, expressed mathematically, is: Ptotal = P₁ + P₂ + P₃ + ...where each subscripted P value is the partial pressure of a different gas.
Air, for example, consists mostly of nitrogen and oxygen, with small quantities of argon, water vapor, and carbon dioxide. The partial pressure of nitrogen accounts for 78 percent of the total pressure exerted by Earth’s atmosphere; oxygen accounts for 21 percent; and argon accounts for 0.9 percent. Together, these three gases account for 99.9 percent of air pressure. Water vapor, carbon dioxide, and all the other trace gases present in the atmosphere combined contribute only a tenth of a percent.

CHARLES LAW

Raising the temperature of a gas causes the gas to fill a greater volume as long as pressure remains constant. Gases expand at a constant rate as temperature increases, and the rate of expansion is similar for all gases. Charles's law (also called Gay-Lussac’s law) describes the relationship between volume and temperature of an enclosed gas. The law says that at constant pressure, the volume of a fixed number of particles of gas is directly proportional to the absolute (Kelvin) temperature, mathematically expressed as: V = k Twhere T is temperature on the Kelvin scale. If the temperature of a given amount of gas is doubled, for example, its volume will also double (as long as pressure remains unchanged).

BOYLE'S LAW

The smaller the volume a given amount of gas is squeezed into, the greater the pressure the gas exerts on the walls of its container. Boyle's law, a mathematical equation that more precisely describes this relationship, states that at constant temperature, the volume of a given quantity of gas varies inversely with the pressure exerted on it. Mathematically, this relationship can be expressed: V is proportional to k (1/P)where V is volume, k is a constant, and P is pressure. Boyle’s law asserts that if the pressure on a given amount of gas is doubled, its volume will decrease by one-half (as long as the temperature of the gas remains unchanged). Conversely, if the pressure is decreased by one-half, the volume will double.

AVOGADRO'S NUMBER

Avogadro’s Number, the number of molecules that exist in one mole, or gram molecular weight, of any substance. One gram molecular weight is the weight of a substance, in grams, that is numerically equivalent to the dimensionless molecular weight of that substance. The number of molecules in one gram molecular weight has been determined to be approximately 6.0221367 × 10²³ molecules, as established by various methods currently available to physical chemists.

The Avogadro number is named in honor of the Italian physicist Amedeo Avogadro, who postulated in 1811 that equal volumes of gases, at equivalent temperatures and pressures, contain the same number of molecules. The theory was significant in the development of chemistry, but the number itself was not calculated until the later 19th century, when the concept was extended to include not only gases but all chemicals . Volume considerations do not apply to liquids or solids, but Avogadro's number itself holds true for all substances, whatever their state.

CONVERSION OF CELSIUS AND FAHRENHEIT

Celsius and Fahrenheit temperatures can be inter converted as follows: 

C = (F - 32) × 100/180 

F = (C × 180/100) + 32.

 Celsius and Kelvin can be inter converted as follows:

C = (K - 273.15) 

K = (C + 273.15).

TEMPERATURE SCALES

Five different temperature scales are in use today: the Celsius scale, known also as the Centigrade scale, the Fahrenheit scale, the Kelvin scale, the Rankine scale, and the international thermodynamic temperature scale. The Celsius scale, with a freezing point of 0° C and a boiling point of 100° C, is widely used throughout the world, particularly for scientific work, although it was superseded officially in 1950 by the international temperature scale. In the Fahrenheit scale, used in English-speaking countries for purposes other than scientific work and based on the mercury thermometer, the freezing point of water is defined as 32° F and the boiling point as 212° F . In the Kelvin scale, the most commonly used thermodynamic temperature scale, zero is defined as the absolute zero of temperature, that is, -273.15° C, or -459.67° F. Another scale employing absolute zero as its lowest point is the Rankine scale, in which each degree of temperature is equivalent to one degree on the Fahrenheit scale. The freezing point of water on the Rankine scale is 492° R, and the boiling point is 672° R.

	Phase Diagram for Water Phase diagrams, like this phase diagram for water, show whether a substance exists as a vapor, liquid, or solid at a given temperature and pressure. The point where the three lines intersect in a phase diagram shows the pressure and temperature where the solid, liquid, and vapor all exist in equlibrium. This point, which occurs for water at 0.01°C (32.02°F), is known as the triple point. Encarta Encyclopedia © Microsoft Corporation. All Rights Reserved.
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In 1933 scientists of 31 nations adopted a new international temperature scale with additional fixed temperature points, based on the Kelvin scale and thermodynamic principles. The international scale is based on the property of electrical resistivity, with platinum wire as the standard for temperature between -190° and 660° C. Above 660° C, to the melting point of gold, 1063° C, a standard thermocouple, which is a device that measures temperature by the amount of voltage produced between two wires of different metals, is used; beyond this point temperatures are measured by the so-called optical pyrometer, which uses the intensity of light of a wavelength emitted by a hot body for the purpose.

In 1954 the triple point of water—that is, the point at which the three phases of water (vapor, liquid, and ice) are in equilibrium—was adopted by international agreement as 273.16 K. The triple point can be determined with greater precision than the freezing point and thus provides a more satisfactory fixed point for the absolute thermodynamic scale. In cryogenics, or low-temperature research, temperatures as low as 0.003 K have been produced by the demagnetization of para magnetic materials. Momentary high temperatures estimated to be greater than 100,000,000 K have been achieved

CATALYSTS

Catalysts are substances that trigger or speed up chemical reactions (without chemically altering the catalysts in the process). A catalyst combines with a reactant to form an intermediate compound that can more readily react with other reactants.

An example of this is the formation of sulfur trioxide (SO₃), which is an important ingredient for producing sulfuric acid (H₂SO₄). Without a catalyst, sulfur trioxide is made by combining sulfur dioxide (SO₂) with molecular oxygen:

 2SO₂ + O₂ → 2SO₃. 

Because this reaction proceeds very slowly, manufacturers use nitrogen dioxide (NO₂) as a catalyst to speed production of SO₃:

Step One: 

NO₂ (catalyst) + SO₂ → NO + SO₃ (SO₃ is extracted and combined with steam to produce sulfuric acid)

Step Two:

 NO (from Step One) + O₂ → NO₂ (catalyst that is reused in step one)

In the above reactions, nitrogen dioxide (NO₂) acts as a catalyst by combining with sulfur dioxide (SO₂) to form both sulfur trioxide (SO₃) and nitrogen monoxide (NO). The sulfur trioxide is removed from the process (to be used in the production of sulfuric acid). Nitrogen monoxide (NO) is subsequently combined with molecular oxygen (O₂) to produce the original catalyst, nitrogen dioxide (NO₂), which can be continually reused to catalyze sulfur trioxide (SO₃₎.

ENTROPY

Entropy is the tendency for matter to become disordered. Nature requires the input of energy to maintain an ordered state—a bedroom will become messy if not periodically cleaned; a car will eventually fall into disrepair if not regularly serviced. Entropy is an important force in chemistry. If other factors influencing a reaction are held equal, a chemical reaction will proceed spontaneously if the products have higher entropy (are more disordered) than the reactants. This law explains why ozone (O₃) gas can spontaneously decompose into molecular oxygen (O₂):

 2O_3(g) → 3O_2(g) 

This reaction occurs because the molecular order is diminished, resulting in a higher level of entropy.

PHYSICAL CONSTANTS

Pi (ratio of a circle’s circumference to its diameter): p = 3.14159265…

e (base of natural logarithms, defined such that ln(e) = 1): e = 2.71828183…

Gravitational constant: G = 6.673 × 10^-11 m³/kg·s²

Acceleration due to Earth’s gravity: g = 9.807 m/s²

Speed of light in a vacuum: c = 299,792,458 m/s (exact)

Avogadro’s constant: N_A=6.022142 × 10²³ mol^-1

Gas constant: R = 8.31447 J/mol·K

Boltzmann constant: k = 1.3806503 × 10^-23 J/K

Planck constant: h = 6.6260688 × 10^-34 J·s

Elementary charge: e = 1.602176 × 10^-19 C

Electron rest mass: m_e = 9.10938189 × 10^-31 kg

Proton rest mass: m_p = 1.67262158 ×10^-27 kg

Neutron rest mass: m_n = 1.6749286 ×10^-27 kg

CELL REACTION AND CELL VOLTAGE

By measuring the potentials of several other standard electrodes versus the standard hydrogen electrode a series of standard electrode potentials can be established. When electrodes involve metals or non metals in contact with their ions, the resulting series is called electromotive series or the list of elements or ions arranged in decreasing order of their standard reduction potential values is called electrochemical series as shown in the following table:

DEFINITIONS

(1) SOLVATION:
                              The process in which solvent molecules surround and interact with solute ions or molecules is called solvation of the solute .

(2) CRYSTALLIZATION:    
                                            When a solution of a compound is concentrated by evaporation of the solvent and then allowed to cool, the solute separates in the form of crystals.The process is called crystallization.

(3) HYDRATED ION:
                                     An ion surrounded by water molecules in an aqueous solution is called hydrated ion.
                     A hydrated ion is surrounded by one or more water molecules.The number of water molecules surrounding an ion depends upon the size and magnitude of charge on the ion e.g Al+++ ion is hydrated easily as compared to CL-.

(4) HYDRATE:
                          When aqueous solution of any salt is evaporated the crystals of the salt separate out with a definite number of water molecules.
                                                                     Such crystalline substances are called Hydrates e.g. MgCl2.6H2O , CuSO4.5H2O and BaCl2.2H2O etc.  
              

HOW TO WRITE A GOOD ESSAY?

To be a good essay writer , you must be able to think and think in an original and independent way .
You must observe things around you and reflect on what you observe.
Let your mind be free to receive impressions to see , hear and feel.
You will not be poor in ideas.
               The two great questions for students who attempt Essay-writing are:

(1)What to say?

(2)How to say it?

The first question is partly answered for you :What to say?
If you have ideas you will know what to say.
You can have a stock of ideas by reading good books ,magazines and so on.
Thinking is very important because thinking over a subject will enable you to give your original point of view on any topic.
Next to the original and striking point of view is the manner or style of expressing it;and that is your second question.How to say it? 
The best style for an essay is the light familiar style.
As we have already observed before , essayists like Lamb and Stevenson have become great on account of their light family style.
So,remember that in an essay you are talking to your readers.
You cannot,however,talk to anybody in a haphazard way.
You must begin your conversation in such a way that you at once arrest the attention of your audience.

HOW WILL YOU BEGIN YOUR ESSAY?

There are different ways in which different essayists begin their essays.Your essay must begin in an interesting way and it is easier to begin indirectly and bring the reader to the main topic in an unexpected way .However, there should be no unnecessary beating about the bush.You may come to the point at once, but do not be abrupt.

HOW WILL YOU PROCEED TO WRITE AN ESSAY?

(1)THINKING:

Think well over the subject and ideas will begin to flow in your mind.

(2)GATHERING MATERIAL: 

Search your memory.If you are able to consult books on the subject,consult them and gather material.

(3)PLANING: 
As you develop your essay,new ideas may crop up.Introduce them in suitable places.

(4)WRITING THE ESSAY:

Next step is to write your essay; remember , you should have three parts in your essay: 
Introduction , Body & Conclusion.
The body itself may be divided into two or three paragraphs as need be.
Use a simple clear language.
 Don't be affected in your style.

(5)REVISION OF THE ESSAY: 

Revise your essay and find mistakes and correct them.

ENGLISH NOTES CLASS XI

REFERENCE , CONTEXT AND EXPLANATION OF

UNDER THE GREENWOOD TREE

Introduction

The lines given for explanation are an extract from the poem Under the Green Wood Tree which is the title of a song taken from the play, As You Like It written by William Shakespeare. The play tells the story of two brothers, the Elder Duke and the younger brother, Duke Frederick. The younger brother is very greedy, selfish and ambitious and wishes to usurp the dukedom. He forces the Elder Duke to go into exile and pass the rest of his life in the forest of Arden. The Elder Duke is accompanied by some his devoted companions and followers. Among them is Lord Amiens, who is gifted with a very sweet, melodious voice. The lines given for explanation are an extract from one of the songs sung by him. In this song, he describes the pleasant and carefree life of the forest. He also extends an open invitation to anyone who wishes to join him in that cheerful surrounding. Such a person should be free from all worldly wishes, and should feel happy and contented to live in the open, natural environment. The only problem one has to face there is the harsh unbearable winter weather.

Lines

UNDER THE GREEN WOOD TREE

WHO LOVES TO LIE WITH ME,

AND TURN HIS MERRY NOTE

UNTO THE SWEET BIRD’S THROAT,

COME HITHER, COME HITHER, COME HITHER:

HERE SHALL HE SEE

NO ENEMY

BUT WINTER AND ROUGH WEATHER

Explanation

In these lines, the singer is giving an open invitation to any one who wishes to join him in the forest of Arden. The singer desires the newcomer to rest under the shady trees and sing a song in such a manner that his voice mingles with the sweet notes of the bird to produce one single harmony. The singer reminds that the life of the forest is free from all enmity and petty rivalries. The only snag in the life of the forest is the unpleasant and unbearable winter wind. If one is brave and willing enough to endure the harshness of the weather, the life of the forest is almost an ideal one.

Lines

WHO DOTH AMBITION SHUN,

AND LOVES TO LIVE I’ THE SUN,

SEEKING THE FOOD HE EATS,

AND PLEASED WITH WHAT HE GETS-

COME HITHER, COME HITHER, COME HITHER,

HERE SHALL HE SEE

NO ENEMY

BUT WINTER AND ROUGH WEATHER

Explanation

In the lines given for contextual explanation, the singer is laying down certain conditions to be fulfilled by one who wishes to come and pass his life in the forest of Arden. In the first place, such a person should have no worldly wishes. He should not be materialistic in his approach and should never run after fame, wealth, power and glory. He should be willing to pass his life in the open atmosphere under the bright sun. He should look for his own sustenance and nourishment and should be contented with whatever he gets to eat. The singer reiterates that the life of the forest is free from all anxieties, problems and difficulties except the unpleasantness of the chilly winter weather.

CLASS XI ENGLISH NOTES

UNDER THE GREENWOOD TREE

SUMMARY

INTRODUCTION TO THE POET:

                                                             William Shakespeare (1564 - 1616) was not only the greatest dramatist in the world of literature but also a renowned odor , and this view of the world as a stage and the most distinguished  poet of Elizabethan period. Although he received a little classic education yet the language of his plays shows that he was well-grounded in Latin and Greek.Shakespeare's genius was fully recognized by his contemporaries.He was really a wonderful poetic craftsman and if you simply speak out his words with a full sense of their meaning and spirit everything will come right.

BACKGROUND OF THE POEM:

                                                          This poem is lyrical charming song taken from his delightful comedy " As You Like It".It occurs in Act II and scene V in it.This short song is sung by Lord Amiens who is attending on the banished Duke,whose dominions have been usurped by his wicked brother Fredrick,as a result of the court intrigues. Lord Amiens praises the forest life.



SUMMARY:
                       In this short song Lord Amiens invites people to spend a very simple life , happy and peaceful life with him in the forest.He praises forest life and says that life in the forest is free and full of pleasures.One can sing a song in the harmony of sweet songs of the birds and may enjoy himself under the green trees.
                                                  Lord prefers the forest life o the court life,because there is no enemy in the forest except winter and rough weather which may cause some trouble, but such things are endurable.If one is not ambitious and wants to live in the open air he may enjoy the forest life.He will have to hunt his own food and be satisfied with what he get.
 He invites people again and again.

Chemistry MCQ'S 3

(1) The number of Significant figures in 5.23*10^23 are 
(a)2 
(b)3 
(c)4 
(d)5
ANSWER: (b)

(2) What would be the decimal equivalent of 1/60 in 3 significant figures 
(a)0.0156 
(b)0.016666 
(c)0.0166 
(d)1.7*10^2
ANSWER: (c)

(3) Any charged particle is called as 
(a)Atom
(b)Ion
(c)Both
(d)N.O.T
ANSWER: (b)

(4) The formula which gives the actual number of atoms is called
(a)Empirical formula 
(b)Molecular formula 
(c)Unit formula 
(d) Structural formula 
ANSWER: (b)

(5) A compound is denoted by _______ mass.
(a)Molecular (b)Atomic (c) Formula (d)Ionic
ANSWER: (c)

(6) 50 g of H2O will possess ______ no: of moles.
(a)2.9 
(b)2.8 
(c)2.7 
(d) 2.6
ANSWER: (c)

(7) 88 g of CO2 contains ______ no: of molecules.
(a)6.02*10^23
(b)12.04*10^23 
(c)6.02*10^11
(d)N.O.T
ANSWER: (b)

(8) When atomic , molecular and formula masses are expressed in grams then they are called as,
(a)Mole fraction 
(b)Mole 
(c) Mass number 
(d) ALL
ANSWER: (b)

(9) 18.06*10^23 atoms of O2 possess ______ grams of mass.
(a)32 g
(b)64 g
(c)96 g
(d)128 g
ANSWER: (c)

(10) Sum of the atomic masses of all atoms present in a compound is called.
(a)Atomic mass 
(b)Formula mass 
(c)Empirical mass
(d)N.O.T
ANSWER: (b)

Chemistry MCQ'S 2

(1)A change in which physical change does not change is called does not change is called ?
(a)Chemical change  
(b) physical change 
(c)Temporary change 
(d) All of them
ANSWER: (b)

(2)Smallest unit of an element which can exist independently is called ?
(a)Atom
(b)ion
(c)Electron
(d)Molecule
ANSWER: (a)

(3) Representation of a chemical change in terms of symbols is called ?
(a)Symbol
(b)Equation
(c)Formula
(d)All
ANSWER: (b)

(4) The formula which gives simplest ration between atoms is called a ____.
(a)Molecular formula 
(b)Empirical formula 
(c)Unit formula 
(d) N.O.T
ANSWER: (b)

(5)The reliable digits in a number that are known with certainty are called  ______.
(a)Important figures
(b)Significant figures 
(c)Numbers 
(d) All of them
ANSWER: (b)

Chemistry MCQ'S 1

(1) Chemistry is about the investigation of __________.
(a)Matter 
(b)Energy 
(c)Both 
(d) None of these
ANSWER: (a)

(2) Quantity of matter contained by a body is called _______.
(a)Density 
(b)volume 
(c)Mass 
(d) All
ANSWER: (c)

(3) A substance in which all the atoms are chemically similar is called _______.
(a)Compound 
(b)Molecule  
(c) Element 
(d) N.O.T
ANSWER: (c)

(4) Which is chemical change among the following ?
(a) Melting of ice 
(b) formation of vapors 
(c) Burning of piece of paper 
(d) N.O.T
ANSWER: (c)

(5) Which is physical change ?
(a) Burning of paper 
(b) burning of piece of paper 
(c) Rusting of iron 
(d) Burning of candle
 ANSWER: (d)