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Atoms and Molecules Class 9 MCQ Chapter 3 Chemistry

Atoms and Molecules Class 9 MCQ with Solutions

1. The ratio by mass of C and O in C{O_2} is :

(A) 1 : 2

(B) 3 : 14

(C)  3 : 8

(D)  3 : 11

Ans.        (C)

Sol.         Ratio by mass of C and O in CO2 =  12 : 32   i.e.  3 : 8.


2.   Law of multiple proportions will remain valid when nitrogen combines with oxygen to form N2O5 and :

(A) N2O

(B) N2O3

(C) N2O4

(D)  All of these

Ans.        (D)

Sol.         In  given examples N2O,  N2O3, N2O4, N2O5

atoms and molecules class 9 mcq

Thus different weight of  O which combine with a fixed weight of N(14g) in all these oxides are in simple whole number ratio and hence supports the law.


3.   When 63.5 g of copper combine with different amount of oxygen to form CuO and Cu2O, the ratio of oxygen combining in two cases is :

(A) 1 : 2

(B) 1 : 1

(C) 79.5 : 143

(D)  2 : 1

Ans.        (D)

Sol.         Ratio of weight of  ‘O’ combining with 63.5g of Cu fixed weight in CuO and Cu2O are different which are found to bear a simple whole number ratio i.e. 16 : 8 = 2 : 1.


4.   The discovery of isotopes & isobars is the failure of :

(A) Law of conservation of mass

(B) Dalton’s atomic theory

(C) Law of multiple proportions

(D) Law of constant proportions

Ans.        (B)

Sol.         On the basic of discovery of isotopes (atoms of same element can have different masses) and isobars  (even atoms of different elements can have the same mass) the postulates of  Dalton’s atomic theory have been discarded.


5.   The balancing of chemical equation is based upon :

(A) Law of combining volumes

(B) Law of multiple proportions

(C)  Law of conservation of mass

(D) Law of definite proportion

Ans.        (C)

Sol.         Balancing of chemical equation is based upon law of conservation  of mass awarding to which matter can neither  be created nor destroyed during any physical or chemical change.


6.   The law of constant composition is applied to :

(A) Any element

(B) Any chemical compound

(C) Pure chemical compound

(D) None of these

Ans.        (C)

Sol.         The law of constant composition is applied to a pure chemical compound as it always contains same  element combined together in the same definite proportion by weight.


7.   The percentage of oxygen in ozone molecule is:

(A) 33.3%

(B) 50.0 %

(C) 75.0 %

(D)100.0%

Ans.        (D)

Sol.         O2 + [O] → O3 % of O in O3 is 100%.


8.    The percentage of hydrogen in water is :

(A) 1.11%

(B)  11.11%

(C) 8.89 %

(D) 88.9 %

Ans.        (B)

Sol.         18 g of H2O contains 2g H2

∴ 100 g of H2O =  \frac{{\rm{2}}}{{{\rm{18}}}} \times 100 = 11.11%


9.   The law of constant composition was given by :

(A) Dalton

(B) Berzelius

(C) Proust

(D)  Lavoisier

Ans.        (C)

Sol.         The law of constant composition was given by proust.


10.   The law of multiple proportions is illustrated by the two compounds :

(A) Sodium chloride and sodium bromide

(B) Ordinary water and heavy water.

(C) Caustic soda and caustic potash

(D)  Sulphur dioxide and sulphur trioxide

Ans.        (D)

Sol.         Law of multiple proportion is illustrated by SO2 and SO3 in which different weight of oxygen (i. e 32 : 48) combining with same weight of sulphur (32g) bear a simple whole number ratio (2 : 3) with one another.


11.   The atomic symbols for Krypton and Antimony are respectively :

(A) Sn and Pb

(B)  Kr and Sb

(C) K and Hg

(D) P and Mn

Ans.     (B)

Sol.        Krypton  = Kr;  Antimony = Sb


12.   The symbol of hydrogen given by Dalton is :

(A)    atoms and molecules class 9 mcq 1

(B)    atoms and molecules class 9 mcq

(C)    atoms and molecules class 9 mcq

(D)    atoms and molecules class 9 mcq

Ans.     (B)

Sol.      Symbol of hydrogen given by Dalton = atoms and molecules class 9 mcq


13.   Dalton’s symbol for nitrogen is :

(A)    atoms and molecules class 9 mcq

(B)    atoms and molecules class 9 mcq

(C)    atoms and molecules class 9 mcq 1

(D)    atoms and molecules class 9 mcq

Ans.     (D)

Sol.      Dalton’s symbol for nitrogen =  atoms and molecules class 9 mcq


14.   Natrium is the latin name of :

(A)  Sodium

(B) Nitrogen

(C) Potassium

(D) Mercury

Ans.     (A)

Sol.      Latin name of Sodium = Natrium.


15.   Stibium is latin name of :

(A) Arsenic

(B) Sulphur

(C) Silicon

(D)  Antimony

Ans.     (D)

Sol.      Latin name of antimony = Stibium.


16.   Buckminster fullerene has the molecular formula of :

(A) C70

(B) C65

(C)  C60

(D) none of the above

Ans.     (C)

Sol.      Molecular formula of Buckminster fullerene = C60


17.   Molecules of helium and phosphorus are :

(A) Monoatomic and triatomic

(B) Monoatomic and diatomic

(C) Diatomic and tetra atomic

(D)  Monatomic and tetraatomic

Ans.     (D)

Sol.      Molecule of Helium =  He monatomic

Molecule of phosphorus = P4 tetratomic


18.  The symbol atoms and molecules class 9 mcq belongs to :

(A) Sulphur

(B)  Mercury

(C) Carbon

(D) Nitrogen

Ans.     (B)

Sol.      Symbol of Mercury = atoms and molecules class 9 mcq


19.   Elements present in lime stone are :

(A) Carbon, hydrogen, oxygen

(B) Calcium, carbon, oxygen

(C) Calcium, oxygen, hydrogen

(D) Calcium, oxygen

Ans.     (B)

Sol.      Elements in limestone CaCO3 = Calcium  + Carbon + oxygen.


20.   Valency of sulphur in sulphur dioxide and sulphur trioxide is ______ and ________respectively :

(A) 3 and 6

(B) 2 and 3

(C) 2 and 6

(D)  4 and 6

Ans.     (D)

Sol.          Valency of S in SO2  = 4, Valency of S in SO3= 6.


21.   Which of the following molecules is not formed by transfer of electrons :

(A) KCI

(B) MgCl2

(C) NaF

(D)  HCl

Ans.     (D)

Sol.      HCl is formed by sharing of electrons.


22.   Which of the following bond in compounds cause highest melting point :

(A)  Ionic bond

(B) Covalent bond

(C) Hydrogen bond

(D) Coordinate bond

Ans.     (A)

Sol.      Ionic bond (electrovalent bond) in compounds causes highest melting point because of three dimensional electrostatic  force between cations  and anions arranged in particular manner.


23.  Compound which is not soluble in water :

(A) NaCl

(B) MgO

(C)  CS2

(D) NaF

Ans.     (C)

Sol.      CS2 is a covalent non-polar compound hence it is not soluble in water.


24.   The term covalent bond was introduced by  :

(A) Thomson

(B) Lavoisier

(C)  Langmuir

(D) None of these

Ans.     (C)

Sol.      Langmuir introduced the term covalent bound.


25.   Number of lone pairs in a molecule of Ammonia :

(A)  1

(B) 2

(C) 3

(D) 4

Ans.     (A)

Sol.      Number of lone pair of electrons in NH3 is 1.

atoms and molecules class 9 mcq =  one lone pair present


26.   Which of the following compound do not contain lone pair :

(A)  CH4

(B) H2O

(C) NH3

(D) None of these

Ans.    (A)

Sol.      (A)   atoms and molecules class 9 mcq   ≡  atoms and molecules class 9 mcq   No. L.P. of e–

(B)     atoms and molecules class 9 mcq      ≡  atoms and molecules class 9 mcq 2 L.P. of e–

(C)     atoms and molecules class 9 mcq   =   atoms and molecules class 9 mcq   one 1. P of e–


27.   Molecule containing only single covalent bond is :

(A) N2

(B) O2

(C) C2H2

(D)  NH3

Ans.     (D)

Sol.      (A) N2 ={\bf{N}} \equiv {\bf{N}}= triple covalent bond

(B) O2 = O = O = double covalent bound

(C) C2H2 = H – C  =  C  – H = double covalent bound between c–atom

(D) NH3 =  atoms and molecules class 9 mcq = Single covalent bound between N and H-atom


28.   Chemical bond is formed between atoms to get :

(A)  Stable electron arrangement

(B) To form ions

(C) Both A and B

(D) None

Ans.     (A)

Sol.      Chemical bond is formed between atoms in order to acquire  stability through gaining or loosing or sharing electrons for stable electronic arrangement.


29.   The bond which is formed by transfer of electrons is :

(A) Covalent bond

(B) Coordinate bond

(C)  Ionic bond

(D) Hydrogen bond

Ans.     (C)

Sol.      Ionic bond is obtained by total transfer of electrons from one atom to another atom.


30.  Electrovalent bond is formed between :

(A) Two metals

(B) Two nonmetals

(C)  A metal and a non metal

(D) two metalloids

Ans.     (C)

Sol.      Electrovalent bond is formed between a metal and a non-metal .  anion e.g.


31.   The number of electrons in outer most shell of non metals are :

(A) 1, 2 or 3

(B) 4, 5 or 6

(C)  5, 6 or 7

(D) 3, 4 or 5

Ans.     (C)

Sol.      Number of electrons in outermost shell of non-metals are 5, 6 or 7.


32.   Bond formed by the sharing of electrons is :

(A) Ionic bond

(B)  Covalent bond

(C) Hydrogen bond

(D) Metallic bond

Ans.     (B)

Sol.      Covalent bond is formed by sharing of equal member of electrons between atoms.


33.   Number of electrons shared between two oxygen atoms in O2  molecule :

(A) 2

(B)  4

(C) 3

(D) 6

Ans.     (B)

Sol.      O2 molecule = atoms and molecules class 9 mcq i.e. electrons (2 pairs of e–) are shared between two oxygen atoms.


34.  Number of lone pair of electrons on nitrogen in HCN is :

(A)  1

(B) 2

(C) 3

(D) 4

Ans.     (A)

Sol.      HC ≡ atoms and molecules class 9 mcq 1 L.P. of e– on N-atom in HCN molecule.


35.   Number of lone pair of electrons on each oxygen atom in CO2  molecule :

(A) 1

(B) 2

(C) 3

(D) 4

Ans.     (B)

Sol.      CO2 = atoms and molecules class 9 mcq = 2 L.P. of e– on each O-atom in CO2 molecule.


36.   Atoms or group of atoms, which are electrically charged, are known as :

(A) Anions

(B) Cations

(C)  Ions

(D) Atoms

Ans.     (C)

Sol.      Ions are atoms or group of atoms which are either positively charged (cation e.g. Na+, NH4+) or negatively charged (Anion e.g. Cl – NO3–).


37.   The charge on cation M is +2 and anion A is –3. The compound has the formula :

(A) MA2

(B)  M3A2

(C) M2A3

(D) M2A

Ans.     (B)

Sol.      M2+A3– = M3A2


38.   Which of the following is the formula of Nickel bisulphate :

(A) NiHSO4

(B) Ni2HSO4

(C) Ni2SO4

(D)  Ni(HSO4)2

Ans.     (D)

Sol.      Nickel bisulphate Ni2+ HSO4– = Ni(HSO4)


39.   Which of the following does not contain electrovalent bond :

(A) K2O

(B)  H2O

(C) MgO

(D) NaCl

Ans.     (B)

Sol.      H2O molecule contains covalent bonding

atoms and molecules class 9 mcq


40.   During the formation of electrovalent bond :

(A) Metal gets reduced

(B) Non metal gets oxidized

(C) Both A and B

(D)  None of these

Ans.     (D)

Sol.      During electrovalent bond formation metal gets oxidised and non-metal gets reduced.


41.   The formula of a chloride of a metal M is MCl3, the formula of the phosphate of metal M will be :

(A) M2(PO4)3

(B) M2PO4

(C) M3PO4

(D)  MPO4

Ans.     (D)

Sol.      In MCl3 metal M is trivalent

∴   Metal M phosphate will be M3+ PO43– = MPO4


42.   The chemical formula of a compound of radium is RaBr2 .The formula of its sulphate is :

(A) Ra(SO4)2

(B) Ra2(SO4)4

(C)  RaSO4

(D) Ra2SO4

Ans.     (C)

Sol.      RaBr2  =  (Ra2+ Br–)

∴    Formula of radium sulphate = Ra2+ SO42– = RaSO4


43.   The formula of chromium sulphite is :

(A) Cr2(SO4)3

(B) Cr3(SO4)2

(C) Cr3(SO3)2

(D)  None of these

Ans.     (D)

Sol.      Formula of chromium sulphate = Cr3+ SO32– = Cr2(SO3)3


44.   Which one of the following is penta-atomic molecule :

(A)  CO2

(B) PCl5

(C) POCl3

(D)  C2H6

Ans.     (C)

Sol.      POCl3 is penta–atomic molecule as it contains 5 atoms.


45.   The valency of cation in cupric sulphate is :

(A) 1

(B)  2

(C) 3

(D) can’t determined

Ans.     (B)

Sol.      Valency of cation (Cu2+) in cupric sulphate CuSO4 is 2 i.e. \mathop {{\rm{C}}{{\rm{u}}^{{\rm{2 + }}}}{\rm{SO}}_{\rm{4}}^{{\rm{2 - }}}}\limits_{{\rm{(cation)}}\,{\rm{(anion)}}}


46.   The molar mass of CH3OH is same as that of :

(A) C2H5OH

(B) H2O

(C) CO

(D)  O2

Ans.     (D)

Sol.      Molar mass of CH3OH = 12  + 3 + 16 + 1 = 32

Which is same at that of O2 = 32

In others molar mass of N2O = 28 + 16 = 44

Molar mass of CO = 12 + 16 = 28

Molar mass of C2H5OH  = 24 + 5 + 16 + 1 = 46


47.    Which of the following represents a polyatomic ion :

(A) Sulphide

(B) Chloride

(C)  Sulphate

(D) Nitride

Ans.     (C)

Sol.      Palyatomic ion is sulphate SO42–

Others are – sulphide S–2, Chloride Cl–, Nitride N3–


48.   An ion is a …………. species :

(A) Positively charged

(B) Negatively charged

(C) Neutral

(D)  either A or B

Ans.     (D)

Sol.      An ion can be either positively charged (e.g. Na+ cation) or negatively charged (e.g. Cl– anion) species.


49.   A cation is :

(A) Negatively charged atom

(B) Neutral atoms

(C)  Positively charged atoms or group of atoms

(D) Negatively charged atom or group of atoms

Ans.     (C)

Sol.      A cation is either positively charged atom (e.g. Na+) or group of atoms (e.g. NH4+).


50.   An anion is :

(A) Positively charged atom

(B) Neutral atoms

(C)  Negatively charged atom or group of atoms

(D) Positively charged atom or group of atoms

Ans.     (C)

Sol.      An anion is either negatively charged atom (e.g.Cl–) or group of atoms (e.g. SO42–).


51.   The no. of sulphur atoms present in one mole of S8 :

(A) 4.018 × 1024

(B)  4.818 × 1024

(C) 4.018 × 1014

(D) None of the above

Ans.     (B)

Sol.        1 molecule of S8 have = 8 S-atom

1 mole of S8 have = 8× 6.02×10 23S-atom

= 4.818 ×1024


52.   The element whose gram – atomic mass and gram – molecular mass are  same is :

(A) Hydrogen

(B) Oxygen

(C) Nitrogen

(D)  Helium

Ans.     (D)

Sol.        Hydrogen  : g atomic mass = 1g
g molecular mass = 2g
Oxygen  : g molecular mass = 16g
g molecular mass = 32g
Nitrogen  : g atomic mass = 14g
g mol. mass = 28g

Helium  : atoms and molecules class 9 mcq


53.   2 g-atom of Aluminium is : (Al = 27) :

(A) 27 u

(B) 54 u

(C) 27 g

(D)  None of  these

Ans.     (D)

Sol.           1 g atom of Al  = 27g

∴ 2g atom of Al  = 27 × 2 = 54 g


54.   One atomic mass unit of carbon-12 is :

(A)  1/12 of the mass of one 12C atom.

(B) 6.022 × 1023 g

(C) 12 g

(D) 1 g

Ans.     (A)

Sol.         1 amu mass  = \frac{{\rm{1}}}{{{\rm{12}}}} of the mass of one c12 atom = \frac{1}{{6.023 \times \,{{10}^{23}}}}

= 1.66 × 10–24g


55.   The mass of 1 a.m.u is :

(A) \frac{1}{{12}} \times \frac{1}{{6.023 \times {{10}^{23}}}}g

(B) \frac{1}{{6.023 \times {{10}^{23}}}}g

(C) \frac{1}{{12}} \times \frac{{12}}{{6.023 \times {{10}^{23}}}}g

(D) 6.023 \times {10^{23}}

Ans.     (B)

Sol.             Mass of 1 a. m.u.  =  \frac{1}{{6.023 \times {{10}^{23}}}}g


56.   The atomic masses of the elements are usually fractional because :

(A) Elements consists of impurities.

(B) These are mixtures of all allotropes

(C) The total number of atoms in a molecule

(D)  These are mixtures of isotopes

Ans.     (D)

Sol.      Atomic masses of the elements are usually fractional because it is average atomic mass as most of the element occur in nature as mixture of several isotopes.


57.   1 mol of CH4  contains :

(A) 6.02 × 1023   atoms of H

(B)  4 g-atom of hydrogen

(C) 1.81 × 1023  molecules of CH4

(D) 3.0 g of carbon

Ans.     (B)

Sol.      1 mole of CH4 contains 4 g atom of hydrogen

= NA molecules by CH4

= 4 NA atoms of H

= NA atoms of C.


58.   Which of the following  has smallest mass :

(A) 4 g of He

(B) 6.022 \times \,{10^{23}}\,atoms of He

(C)  1 atom of He

(D) 1 mole of He

Ans.     (C)

Sol.      (i) 4g He

(ii) 6.022 × 1023 atoms of He = 4g of He

(iii) 6.023 × 1023 atoms of He  = 4g

∴   1 atom of the = \frac{{\rm{1}}}{{{\rm{6}}{\rm{.023 \times 1}}{{\rm{0}}^{{\rm{23}}}}}}{\rm{g  = }}\mathop {\frac{{\rm{4}}}{{{{\rm{N}}_{\rm{A}}}}}g}\limits_{{\rm{Smallest mass}}}

1 mole of He = 4g of He


59.  How many grams are present  in 1 gram atom of sodium :

(A) 23 g

(B) 13 g

(C) 1 g

(D) \frac{1}{{23}}g

Ans.     (A)

Sol.      1 g atom of NA ≡ 1 mole of Na ≡ 23 g of Na


60.  Weight of 1 atom of hydrogen is :

(A)  1.66 \times \,{10^{ - 24}}g

(B) {10^{22}}\,g

(C) {10^{ - 22}}\,g

(D) 1 \times {10^{ - 23}}\,g

Ans.     (A)

Sol.            wt. of 1 atom of H  = \frac{1}{{6.023 \times {{10}^{23}}}}  = 1.66 × 10–24g

 

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