Smallest particle into which matter can be divided.

The combining power (or capacity) of an element.

MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 2

Which scientist suggested that the symbols of elements should be made of one or more letters of the names of the elements?

0%
Dalton
0%
Rutherford
0%
Lavoisier
0%
Berzelius

Explanation

Berzelius was the scientist who suggested that the symbols should be made of the first or first two letters of the names of the elements.

Hence, the correct option is

$D$ .

What is the atomic mass (u) of sodium?

0%
22
0%
23
0%
23.5
0%
24

Explanation

Sodium is a chemical element with the symbol

$Na$ and atomic number

$11$ . Atomic mass (u) of sodium =

$23u$ .

It is a soft, silvery-white, highly reactive metal.

The sum of mass of all the atoms in a molecule is known as :

0%
molecular mass
0%
mass number
0%
atomic weight
0%
None of above

Explanation

The sum of the atomic masses of all the atoms present in a molecule is known as molecular mass. It is therefore a relative mass of a molecule expressed in atomic mass units (u).

For example- molecular mass of carbon dioxide is 44 u and it is calculated as below

The atomic mass of carbon =

$12\ u$ and

The atomic mass of oxygen =

$16\ u$

$\therefore$ molecular mass of

$CO_2 = (1\times atomic\ mass\ of\ C) + (2\times atomic\ mass\ of\ O)$

Molecular mass of

$CO_2 = (1\times \ 12) + (2\times 16) = 44\ u$

The correct option is A.

Atoms of same element combines to form:

0%
molecules
0%
ions
0%
large atoms
0%
compounds

Explanation

If two or more atoms of the same element combine, they produce a molecule.

for example:

$H_2, O_3$

Hence, the correct option is A.

The unit, mole, was accepted in the year?

0%
1962
0%
1965
0%
1967
0%
1969

A negatively charged ion in a compound is called a/an:

0%
electron
0%
valency
0%
cation
0%
anion

Explanation

The negatively charged ion is known as anion.

For example,

$Cl^-$ is the anion of a chlorine atom and we called it a chloride ion.

The word mole was introduced by ______ in _______.

0%
Avogadro, 1897
0%
Dalton, 1896
0%
Wilhelm Ostwald, 1896
0%
Proust, 1897

One mole is equal to number of atoms as contained in:

0%
1 g of carbon
0%
6 g of carbon
0%
12 g of carbon
0%
12 kg of carbon

Explanation

One mole is equal to number of atoms as contained in 12 g of carbon, i.e. 6.022

$\times$ 10

$^{23}$ atoms.

The symbol of potassium is taken from :

0%
kalium
0%
kappa
0%
kamenikeia
0%
kassandrenos

French chemist ____ laid the foundation to the scientific investigation of matter by describing that substances react by following certain laws.

0%
Dalton
0%
Rutherford
0%
Antony van Leeuwenhoek
0%
A. Lavoisier

The laws of chemical combination formed on the basis of :

0%
Dalton's atomic theory
0%
Dalton's mass theory
0%
Both A and B
0%
None of the above

The correct symbol of metal cobalt is:

0%
$Sd$
0%
$De$
0%
$Co$
0%
$Pn$

Explanation

Cobalt is a chemical element with symbol

$Co$ and atomic number

$27$ .

Atoms are:

0%
indivisible
0%
divisible
0%
may be divisible
0%
None of the above

The word 'atom' is derived from the Greek word ____________.

0%
atomic
0%
atomos
0%
atomey
0%
atomoney

_____ are the basic units of matter and the defining structure of elements.

0%
Compounds
0%
Atoms
0%
Ions
0%
None of these

........... are made up of atoms that are held together by chemical bonds.

0%
Elements
0%
Molecules
0%
Mixtures
0%
Both A and B

Definition of anion is :

0%
Negatively charged ion
0%
Positively charged ion
0%
Neutral ion
0%
None of the above

Explanation

Ions are atoms or molecules that have an electrical charge. Ions can have either a positive or negative charge, and ions with a negative charge are known as

$anions.$
Option (A) is correct.

The discovery of __________ proved that atom is divisible.

0%
atoms
0%
sub-atomic particles
0%
elements
0%
isotope

What is a molecule?

0%
A group of two or more atoms that are chemically bonded together.
0%
Smallest particle into which matter can be divided.
0%
The combining power (or capacity) of an element.
0%
Both A and B.

Explanation

A group of two or more atoms that are chemically bonded together or are tightly held together by attractive forces is known as a molecule.
The smallest particle into which a matter can be divided is known as an atom.
The combining power of an element is known as its valency.

So, the correct option is

$A$

According to Dalton, atoms of different elements combine with one another to form:

0%
compounds
0%
elements
0%
solution
0%
All of the above

Explanation

According to Dalton, atoms of different elements combine with one another to form compounds.

For example;

$H + Cl \rightarrow HCl$

When atoms of one element are combined with atoms of another element, the result is a(n) _________ of a compound.

0%
electron
0%
ion
0%
molecule
0%
enzyme

Explanation

When atoms of one element are combined with atoms of another element, the result is a molecule of a compound. For example, a

$C$ atom combines with an

$O$ atom to form a

$CO$ molecule. Thus, a compound is obtained by a combination of atoms of different elements.

Cations carry a ___________ charge.

0%
positive
0%
negative
0%
no charge
0%
none of these

Explanation

$(A)$ positive

The cation is an ion that carries a positive charge, causing it to migrate to the cathode during the electrolysis of salts. It has more protons than electrons, resulting in a positive charge.

Tungsten is a metal used in the filament of incandescent bulbs. What is the chemical symbol of Tungsten?

0%
W
0%
Tn
0%
Tu
0%
Wo

Which one of the following scientist's proposed the law of conservation of mass?

0%
J.J. Thomson
0%
John Dalton
0%
Rutherford
0%
Berzelius

Explanation

The law of conservation of mass is given by John Dalton which states that mass can neither be created nor be destroyed in a chemical reaction.
option

$B$ is correct.

Molecular mass of

$Ca(OH)_2$ is :

0%
$61$
0%
$57$
0%
$74$
0%
None of above

Explanation

Molecular mass of

$Ca(OH)_2 = 1$ (Atomic mass of

$Ca$ )

$+ 2$ (Atomic mass of

$O$ )

$+ 2($ Atomic mass of

$H)$

$= 40 + 2(16) + 2(1)$

$= 40 + 32 + 2$

$= 74$

State the atomic mass of

$H_2O$ ?

0%
$16$ u
0%
$17$ u
0%
$18$ u
0%
$15$ u

Explanation

Atomic mass of hydrogen is

$1\ u$ and oxygen is

$16\ u$ .
Hence molecular mass of water

$(H_2O)=(2\times 1)\ u + 16\ u = 18\ u$

Option

$C$ is correct.

Hydrogen atom has an approximate diameter of:

0%
$10^{-9}\ m$
0%
$10^{-10}\ m$
0%
$9^{-10}\ m$
0%
$10^{-11}\ m$

Explanation

A hydrogen atom has a diameter of approximately

$1.06 \times {10}^{-10} \; m \approx {10}^{-10} \; m$ , as defined by the diameter of the spherical electron cloud around the nucleus.

A symbol of an element represents:

0%
one atom of the element
0%
one molecule of the element
0%
all the atoms of the element
0%
all the molecules of the element

Indicate whether the following statement is true or false.
Molecules can exist independently.

0%
True
0%
False

Indicate whether the following statement is true or false.
Molecules combine to form atoms.

0%
True
0%
False

$10.0\ g$ of

$CaCO_{3}$ on heating gave

$4.4\ g$ of

$CO_{2}$ and

$5.6\ g$ of

$CaO$ . This observation is in agreement with the:

0%
law of constant composition
0%
law of multiple proportion
0%
law of reciprocal proportion
0%
law of conservation of mass

Explanation

$CaCO_{3}\rightarrow CaO + CO_{2}$
10 gm 5.6 gm 4.4 gm

Mass of

$CaCO_{3}\: (10\ gm) =$ Mass of

$CaO\ (5.6\ gm)$ + Mass of

$CO_{2}\ (4.4\ gm)$

Hence, it proves the law of conservation of mass.

The weight of gaseous mixture containing

$6.02 \times 10^{23}$ molecules of nitrogen and

$3.01\times 10^{23}$ molecules of sulphur dioxide is:

0%
46
0%
92
0%
60
0%
30

Explanation

The molar masses of nitrogen and sulphur dioxide are

$28$ g/mol and

$32$ g/mol respectively.

$6.02 \times 10^{23}$ molecules of nitrogen corresponds to

$1$ mole or

$28$ g.

$3.01\times 10^{23}$ molecules of sulphur dioxide corresponds to

$0.5$ mole or

$32$ g.
Hence, the weight of the gaseous mixture is

$28 \: g + 32 \: g = 60 \: g$ .

Number of atoms in

$558.5$ gram Fe is:

[Atomic mass of

$Fe = 55.85\ u$ ]

0%
twice that of 60 g carbon
0%
$6.023\times 10^{22}$
0%
half that in $8$ g He
0%
$558.5\times6.023\times 10^{23}$

Explanation

Number of moles of Fe atoms =

$\dfrac {Mass}{Atomic\ mass}$

$=\dfrac {558.5}{55.85} = 10$

558.5 g of Fe corresponds to 10 moles of Fe and has

$10N_{A}$ atoms of Fe.

Option A - 12 g of carbon means Avogadro's number, therefore, 60 g of carbon means, 5 moles of carbon and thus contains

$5\times N_{A}$ atoms, twice of this equals

$10 N_{A}$ atoms.

Option B -

$\dfrac{N_{A}} {10}$ atoms.

Option C - 8 g of He corresponds to 2 moles of He and thus, contains

$2N_{A}$ atoms, half of the atoms will be

$N_{A}$ atoms of He.

So, option A only corresponds to number of atoms in 558.5 g Fe, i.e.

$10N_A$ atoms.

Which of the following has highest mass?

0%
$50$ g of iron
0%
$5$ moles of nitrogen gas
0%
$5 \times 10^{23}$ atoms of carbon
0%
All are equal

Explanation

$Number\ of\ moles = \dfrac {Mass}{Molar\ mass}$

$\therefore Mass = Number\ of\ moles\ \times molar\ mass$

To calculate the mass of 5 moles of nitrogen gas, we have first find out its molar mass.

So, molar mass of

$N_2 = 2 \times 14 = 28\ g/mol$

$Mass\ of\ 5\ moles\ of\ N_2 = Number\ of\ moles\ \times molar\ mass$

$= 5 \times 28 = 140\ g$

Option B (140 g) is greater than option A (50 g).

Let's now compare with option C (

$5 \times 10^{23}$ atoms of carbon)

$Number\ of\ moles = \dfrac {Given\ number\ of\ particles}{Avogadro\ number}$

$Mass = Number\ of\ moles\ \times molar\ mass$

$\therefore Mass = \dfrac {Given\ number\ of\ particles}{Avogadro\ number} \times molar\ mass$

$= \dfrac {5 \times 10^{23}}{ 6.022 \times 10^{23}} \times 12 = 19.96\ g$

So, mass of option B is higher than both option A and option C.

$10$ grams each of

$O_{2},\ N_{2}$ and

$Cl_{2}$ are kept in three bottles. The correct order of arrangement of bottles containing decreasing number of molecules is:

0%
$O_{2} >\ N_{2}>\ Cl_{2}$
0%
$Cl_{2}>\ N_{2}>\ O_{2}$
0%
$Cl_{2}>\ O_{2}>\ N_{2}$
0%
$N_{2}>\ O_{2}>\ Cl_{2}$

Explanation

No. of molecules

$=\displaystyle \dfrac{Weight}{Molecular\ Weight}\times N_A$

Molecular weight order is

$Cl_2 > O_2 > N_2$ .

Therefore, the order of no. of molecules is

$N_{2}>O_{2}>Cl_{2}$ .

Hence, option

$D$ is correct.

Irrespective of the source, a pure sample of water always yields

$88.89\%$ oxygen by mass and

$11.11\%$ hydrogen by mass. This is explained by the law of:

0%
conservation of mass
0%
constant proportion
0%
multiple proportion
0%
none of these

Explanation

The molecular mass of water is 18 amu.

Molecular mass of oxygen is 16 amu. So, % of oxygen in

$H_2O$ is

$\dfrac{16}{18}\times 100= 88.89 \%.$ .

Molecular mass of hydrogen is 2 amu. So, % of hydrogen in

$H_2O$ is

$\dfrac{2}{18}\times 100= 11.11\%.$ .

According to the law of constant proportions, a chemical compound always contains the same elements combined in the same proportion by mass. For example, pure water obtained from different sources such as rivers, wells, springs, seas, etc., always contains hydrogen and oxygen together in the ratio of 1:8 by mass.

$8$ g of

$O_{2}$ has the same number of molecules as:

0%
7 gms of $CO$
0%
14 gms of $CO$
0%
22 gms of $CO_{2}$
0%
44 gms of $CO_{2}$

Explanation

Moles of

$O_2 = \dfrac{8}{32} = 0.25$ moles

$No.\ of\ molecules$

$= No.\ of\ moles \times N_{A}$ .

Thus, no. of moles is directly proportional to no. of molecules.

Moles of

$7$ gm

$CO = \dfrac{7}{28} = 0.25$

Moles of

$14$ gm

$CO = \dfrac{14}{28} = 0.5$

Moles of

$22$ gm

$CO_{2} = \dfrac{22}{44} = 0.5$

Moles of

$44$ gm of

$CO_{2} = 1$

Hence, option A is correct.

Choose the correct option for the following statement.

The use of

$^{12}C$ scale has superseded the older scale of atomic mass based on

$^{16}O$ isotope, one important advantage of the former being:

0%
The atomic masses on $^{12}C$ scale became whole numbers.
0%
$^{12}C$ is more abundant in the earths crust than $^{16}O$ .
0%
The difference between the physical and chemical atomic masses got narrowed down significantly.
0%
$^{12}C$ is situated midway between metals and non-metals in the periodic table.

Explanation

Physical stuck to pure $^{16}O$ for mass scale and chemistry used an average of all three isotopes because natural oxygen is the mixture of $^{16}O$ , $^{17}O$ and $^{18}O$ . There was not much difference on average.

But with molecules of 200-500 amu, it starts to add up. Use of $^{12}C$ which is isotopically pure, get narrow down the difference between physical and chemical atomic masses.

The number of molecules present in

$4.4$ g of

$CO_{2}$ gas is:

0%
$6.022\times 10^{23}$
0%
$5.022\times 10^{23}$
0%
$6.022\times 10^{24}$
0%
$6.022\times 10^{22}$

Explanation

1 mole of

$CO_2$ have

$6.022\times10^{23}$ molecules.

Weight of one 1 mole of

$CO_2$ = 44g(molar mass).

Number of moles =

$\dfrac {given \ mass}{molar \ mass}$ .

Number of moles of

$CO_2$ in 4.4 g =

$\dfrac{4.4}{44}=0.1$ .

So, number of molecules in 4.4g of

$CO_2$ =

$\dfrac{6.022\times10^{23}}{44}\times4.4 = 6.023 \times10^{22}$ .

Which of the following is the best example to demonstrate the law of conservation of mass?

0%
12 gm of carbon combines with 32 gm of oxygen to form 44 gm of $CO_{2}$ .
0%
When 72 gm of carbon is heated in a vacuum and no change in its mass takes place.
0%
The weight of a piece of platinum is the same before and after heating in air.
0%
None of these

Explanation

According to the law of conservation of mass:

The total mass of the reactant = the total mass of the product.

Mass of reactants

$= 12 + 32 = 44$ i.e w(C)+ w(oxygen)

Mass of products

$= 44$ i.e. w(carbon dioxide)

Both B and C do not represent a chemical reaction, but only heating of elements, hence they are not the best examples to demonstrate the law of conservation of mass.

When equal masses of methane and sulphur dioxide are taken, then the ratio of their molecules is:

0%
1 : 1
0%
1 : 2
0%
2 : 1
0%
4 : 1

Explanation

The molecular weights of methane and sulfur dioxide are

$16$ and

$64$ respectively. The ratio of their molecules is equal to the ratio of their moles. For equal masses of methane and sulphur dioxide, we know that the number of moles is inversely proportional to the molecular weight.

$\dfrac { Molecules\quad of\quad CH_4 }{ Molecules\quad of\quad SO_2 }$

$=\dfrac { Moles\quad of\quad CH_4\times N_A }{ Moles\quad of\quad SO_2\times N_A }$

$=\dfrac { Mol\quad wt.\quad of\quad SO_2 }{ Mol\quad wt.\quad of\quad CH_4 } =\dfrac { 64 }{ 16 } =4:1$

Which one of the following contains a same number of atoms as there are in 12 grams of magnesium?

0%
12 grams of carbon
0%
40 grams of calcium
0%
16 grams of oxygen
0%
7 grams of carbon monoxide

Which of the following gases contain the same number of molecules as that of

$16$ g of oxygen?

0%
$16$ g of $O_{3}$
0%
$32$ g of $SO_{2}$
0%
$16$ g of $SO_{2}$
0%
None of these

Explanation

Number of molecules = Number of moles

$\times N_A$

When two gases have the same number of molecules, they will contain the same number of moles.

Number of moles of a substance=

$\dfrac{give\ mass}{molar\ mass}$

$16$ g of oxygen

$(O_2$ ) corresponds to

$\dfrac{16}{32} = 0.5$ mole.

$16$ g of

$O_3$ corresponds to

$\dfrac{16}{48} = 0.33$ mole.

$32$ g of

$SO_2$ corresponds to

$\dfrac{32}{64} = 0.5$ mole.

$16$ g of

$SO_2$ corresponds to

$\dfrac{16}{64} = 0.25$ mole.

Hence, option B is correct.

$4.6\times 10^{22}$ atoms of an element weight

$13.8$ g. What is the atomic mass of the element?

0%
290 u
0%
180.6 u
0%
34.4 u
0%
104 u

Explanation

$1$ mole of any substance contains

$6.02 \times 10^{23}$ atoms.

Thus,

$4.6 \times 10^{22}$ atoms corresponds to

$\dfrac{4.6 \times 10^{22}}{6.022 \times 10 ^{23}}=0.0764$ moles.

$0.0764$ moles weighs

$13.8$ g.

Thus,

$1$ mole will weigh

$\dfrac{13.8}{0.0764}= 180.6 \ g$ .

Hence, the atomic mass of the element will be 180.6 u.

The ratio of the mass of a C-12 atom to that of an atom of element X (whose atomicity is four) is

$1: 9$ . The molecular mass of element X is :

0%
$480\ gmol^{-1}$
0%
$432\ gmol^{-1}$
0%
$36\ gmol^{-1}$
0%
$84\ gmol^{-1}$

Explanation

The mass of one mole of carbon-12 is 12 g.
The mass of one mole of X atoms will be

$9 \times 12 = 108$ g.

But here atomicity of

$X$ is 4.
Thus, one molecule will contain

$4X$ atoms.

Hence, the mass of one mole of the compound will be

$4 \times 108 = 432$ g. This is the molecular weight.

Hence, option

$B$ is correct.

The weight of one molecule of

$C_{60} H_{122}$ is:

0%
$1.2\times 10^{-20}g$
0%
$5.025\times 10^{23}g$
0%
$1.4\times 10^{-21}g$
0%
$6.023\times 10^{23}g$

Explanation

The molecular weight of

$C_{60}H_{122}$ is

$842$ g/ mol.

One mole of

$C_{60}H_{122}$ weighs

$6.02 \times 10^{23}$ g.

Thus, weight of one molecule of

$C_{60}H_{122}$ is

$\dfrac { 842 }{ 6.02 \times 10^{ 23 } } = 1.4 \times 10^{-21} g$ .

Hence, option

$C$ is correct.

Which of these has the maximum number of molecules?

0%
$7$ g $N_{2}$
0%
$2$ g $H_{2}$
0%
$16$ g $NO_{2}$
0%
$16$ g $O_{2}$

Explanation

$\bf{Hint-}$

$1$ mole of any compound containd

$N_A$ molecules.

$\bf{Formula\ used-}$

The expression for the number of molecules is given as:

$Number\: of\: molecules=\dfrac { Mass}{ Molecular\: mass } \times N_A$ ,

where

$N_A$ is the Avogadro number.

$\bf{Explanation-}$

$\bullet$

$N_2 \: contains\: \dfrac { 7\times N_A }{ 28 } =0.25 \times N_A\: molecules$

$\bullet$

$H_{ 2 }\: contains\: \dfrac { 2\times N_A }{ 2 } =1 \times\ N_A\: molecules$

$\bullet$

$NO_{ 2 }\: contains\: \dfrac { 16\times N_A }{ 46 } =0.35 \times N_A\: molecules$

$\bullet$

$O_{ 2 }\: contains\: \dfrac { 16\times N_A }{ 32 } = 0.5 \times N_A\:molecules$

$\bf{Final\ answer-}$

$B$

Which of the following contains highest number of atoms?

0%
4 gm of oxygen
0%
4 gm of carbon dioxide
0%
4 gm of helium
0%
4 gm of methane

Explanation

No. of molecules

$= No.\ of\ moles \times \ N_A$

$= \dfrac {Mass}{Molar\ mass} \times \ N_A$

No. of atoms

$= \dfrac {Mass}{Molar\ mass} \times \ N_A \times No.\ of\ atoms\ in\ 1\ molecule$

Option A: Number of atoms in 4 g oxygen

$O_2$

$=\dfrac{4}{32} \times N_A \times 2 = \dfrac{N_A} {4}$

Option B: Number of atoms in 4 g carbon dioxide

$CO_2$

$=\dfrac{4 }{44} \times N_A\times 3 = \dfrac{N_A} {3.67}$

Option C: Number of atoms in 4 g helium

$He$

$=\dfrac{4}{4} \times N_A \times 1= \dfrac{N_A} {1}$

Option D: Number of atoms in 4 g methane

$CH_4$

$=\dfrac{4 }{16} \times N_A \times 5 = \dfrac{N_A} {0.8}$

Arranging in the order of increasing number of atoms:

$\dfrac{N_A} {4}$ <

$\dfrac{N_A} {3.67}$ <

$\dfrac{N_A} {1}$ <

$\dfrac{N_A} {0.8}$

Hence option

$D$ is the correct option having highest number of atoms.

Different samples of water were found to contain hydrogen and oxygen in the ratio of 1 : 8 by mass. This proves the law of:

0%
multiple proportion
0%
constant proportion
0%
reciprocal proportion
0%
conservation of mass

The maximum number of molecules are present in:

0%
$36$ g $H_{2} O$
0%
$28$ g $CO$
0%
$46$ g $C_{2} H_{5} OH$
0%
$54$ g $N_{2} O_{5}$

Explanation

Number of molecules = Number of moles

$\times N_A$

$= \dfrac {\text{given mass}} {\text{molar mass}}\times N_A$

The more the number of moles, the more will be the number of molecules.

$36$ g of water(

$H_2O$ ) corresponds to

$\dfrac{36}{18} = 2$ moles (Molar mass 18

$g\ mol^{-1}$ ).

$28$ g of

$\ CO$ corresponds to

$\dfrac{28}{28} = 1$ mole (Molar mass 28

$g\ mol^{-1}$ ).

$46$ g ethanol(

$C_2H_5OH$ ) corresponds to

$\dfrac{46}{46} = 1$ mole (Molar mass 46

$g\ mol^{-1}$ ).

$54$ g dinitrogen pentoxide(

$N_2O_5$ ) corresponds to

$\dfrac{54}{108} = 0.5$ moles (Molar mass 108

$g\ mol^{-1}$ ).

Hence, option A is correct.

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 2 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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