Atoms and Molecules Class 9 MCQ for Students 2025

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Atoms and Molecules Class 9 Objective MCQ for Students

Quick Quiz

Which of the following is/are correct for the law of constant proportion? 1. It was given and stated by Lavoisier. 2. In a chemical substance, the elements are always present in definite proportions by mass.

(a) Only 1

(b) Only 2

(d) Neither 1 nor 2

Option b – Only 2

Which of the following is/are true for Dalton’s atomic theory? 1. All matter is made of tiny up very particles called atoms. 2. Atoms do not participate in chemical reactions. 3. Atoms are indivisible particles.

(a) 1 and 2

(b) 2 and 3

(d) 1, 2, and 3

Option c – 1 and 3

Which of the following is/are correct for molecules? 1. It is a group of two or more atoms that are chemically bonded together. 2. Atoms of only the same element join to form molecules. ( Atoms and Molecules Class 9 Objective )

(a) Only 1

(b) Only 2

(d) Neither 1 nor 2

Option a – Only 1

Which of the following are correctly matched? 1. Argon – monoatomic 2. Phosphorus – polyatomic 3. Chlorine – diatomic

(a) 1 and 2

(b) 2 and 3

(d) 1, 2, and 3

Option c – 1 and 3

Which of the following is/are correct for ions? 1. The charged species are known as ions. 2. A negatively charged ion is called a cation. 3. A group of atoms carrying a charge is known as a polyatomic ion.

(a) 1 and 2

(b) 2 and 3

(d) 1, 2, and 3

Option c – 1 and 3

Which of the following is/are correct for atomic mass? 1. It was proposed by Bohr. 2. It was explained by the law of constant proportions. ( Atoms and Molecules Class 9 Objective )

(a) Only 1

(b) Only 2

(d) Neither 1 nor 2

Option b – Only 2

………. represents the atoms and ………. represents molecular and compounds.

1) Names of formula

2) symbols & formula

3) formula & symbols

4) Names & valency

Option 2 – symbols & formula

What is the symbol of sodium ( Atoms and Molecules Class 9 Objective )

1) S

2) Na

3) K

4) Sd

Option 2 – Na

Latin word for water is

1) Hydro

2) Helios

3) Hydrogen

4) Oxy

Option 1 – Hydro

The gas which was first discovered in the sun

1) Hydrogen

2) Oxygen

3) Helium

4) Nitrogen

Option 3 – Helium

Law of definite proportion was given by ( Atoms and Molecules Class 9 Objective )

1) John Dalton

2) Lavoisier

3) Joseph Proust

4) Ritcher

Option 3 – Joseph Proust

Among the following the elements that are discovered and named after scientist

1) Einsteinium

2) Fermium

3) Rutherfordium and Mendelevium

4) all the above

Option 3 – Rutherfordium and Mendelevium

Law of conservation of mass was proposed by

1) Landolt

2) Lavoisier

3) Dalton

4) Proust

Option 2 – Lavoisier

Law of conservation of mass was experimentally verified by ( Atoms and Molecules Class 9 Objective )

1) Lavoisier

2) Landolt

3) Proust

4) Berzelius

Option 2 – Landolt

” A given chemical substance always contains the same elements combined in a fixed proportions by weight ” is called

1) Law of conservation of mass

2) Law of constant proportions

3) Law of definite proportions

4) both b & c

Option 2 – Law of constant proportions

Which postulate of Dalton’s theory is the result of law conservation of mass ( Atoms and Molecules Class 9 Objective )

1) matter can be neither created nor destroyed

2) atoms of different elements or different in properties

3) atoms similar elements or similar in properties

4) atoms is a smallest particle take part in chemical reactions

Option 1 – matter can be neither created nor destroyed

An element X forms the oxides containing 57.7% and 42.3% of Oxygen respectively. This indicates the law of

1) Definite proportions

2) Multiple proportions

3) Reciprocal proportions

4) None of these

Option 2 – Multiple proportions

A …….. is the smallest particle of an element or a compound that is capable of independent existence and retain all the properties of that substance. ( Atoms and Molecules Class 9 Objective )

1) Molecule

2) Compound

3) Atom

4) Mixture

Option 1 – Molecule

Mass of one mole of a substance is called

1) Atomic mass

2) Molecular mass

3) Molar mass

4) Unit mass

Option 3 – Molar mass

The total mass of the products formed in a chemical reaction is exactly equal to the mass of the reactants. This is known as

1) Law of conservation of mass

2) Law of multiple proportions

3) Law of definite proportions

4) None of these

Option 1 – Law of conservation of mass

In a chemical substance the elements are always present in fixed proportions by mass. This is known as the : ( Atoms and Molecules Class 9 Objective )

1) Law of conservation of mass.

2) Law of multiple proportions

3) Law of definite proportions

4) None of these

Option 3 – Law of definite proportions

An ………. is the smallest particle of an element that can participate in chemical reaction and retain all its properties.

1. Molecule

2) Compound

3) Atom

4) Mixture

Option 3 – Atom

The number of atoms constituting a molecule is known as its ( Atoms and Molecules Class 9 Objective )

1) Valency

2) Combining power

3) Atomicity

4) none

Option 3 – Atomicity

Which of the following is mono atomic

1) Hydrogen

2) Ozone

3) Nitrogen

4) Helium

Option 4 – Helium

The symbol for the element chromium is

1) Cr

2) Cl

3) C

4) Ca

Option 1 – Cr

Greek name for sun is ( Atoms and Molecules Class 9 Objective )

1) Hydro

2) Oxy

3) Helio

4) Helios

Option 3 – Helio

Which of the following does not change when a chemical reaction takes place

1) Volume

2) Mass

3) physical properties

4) chemical properties

Option 2 – Mass

Molecules of the following element are made up of only one atom of that element ( Atoms and Molecules Class 9 Objective )

1) Iron

2) Sodium

3) Helium

4) Chlorine

Option 3 – Helium

Argon is

1) monoatomic

2) diatomic

3) triatomic

4) polyatomic

Option 1 – monoatomic

Which of the following is not the postulate of Dalton’s atomic theory of matter ( Atoms and Molecules Class 9 Objective )

1) Each element is made up of extremely small particles called atoms

2) Atoms of a given element are identical in chemical properties but may have be different physical properties

3) Atoms cannot be created or destroyed

4) Compounds are formed by the chemical union of atoms of two or more elements in a fixed proportion which are simple whole number

Option 2 – Atoms of a given element are identical in chemical properties but may have be different physical properties

Matter consists of indivisible particles called

1) Molecules

2) Compounds

3) Elements

4) Atoms

Option 4 – Atoms

When the particles of a substance contain only one type of atoms, the substance is called

1) Element

2) Compound

3) Molecule

4) None

Option 1 – Element

Choose the odd molecule

1) Argon molecule

2) Chlorine molecule

3) Oxygen molecule

4) Fluorine molecule

Option 1 – Argon molecule

Bohr,s theory is valid for

1) All atoms

2) All ions

3) Any atom or ion having single electron

4) All molecules

Option 3 – Any atom or ion having single electron

The sub-shells present in L- shell are

1) s and d

2) s and p

3) s,p and d

4) s,p,d and f

Option 2 – s and p

Rutherford suggested that atoms are

1) spherical

2) cylindrical

3) tetrahedral

4) pyramidal

Option 1 – spherical

Bohr’s model could not account for

1) Seebeck effect

2) Raman’s effect

3) Condensation effect

4) Zeeman effect

Option 4 – Zeeman effect

The region in space where there is a finite probability of finding electron is

1) Atomic number

2) Atomic orbital

3) Atomic particle

4) Ground state

Option 2 – Atomic orbital

Gold foil was used in Rutherford’s scattering experiment because it

1) has high refractive index

2) has high density

3) is highly malleable

4) is high ductile

Option 3 – is highly malleable

According to Bohr Burry the maximum number of electrons that can be accommodated in each atomic orbital is

1) 8

2) 2

3) 10

4) 6

Option 2 – 2

Atomic number of A is 10 and element B is 11. Which statement about A and B is correct

1) Both are chemically inert

2) B is chemically inert

3) B is more reactive than A

4) A is more reactive than B

Option 3 – B is more reactive than A

Isotopes are

1) atoms of same element

2) atoms of different elements

3) molecules of same element

4) radicals of the same element

Option 1 – atoms of same element

Isobars have

1) same no. of protons and different electron

2) different number of protons and neutrons

3) same no. of electrons and neutrons

4) same no. of neutrons

Option 2 – different number of protons and neutrons

The orbits of an atom are also called energy levels because these are spheres containing definite energy.

1) assertion is correct and reason is correct

2) assertion is correct but reason is wrong

3) assertion is wrong but reason is correct

4) assertion is wrong and reason is wrong

Option 2 – assertion is correct but reason is wrong

The size of an atom is decided by

1) mass of the atom

2) no. of protons

3) no. of protons and neutrons

4) no. of electrons

Option 4 – no. of electrons

Calcium has 20 electrons. These occupy K,L,M, and N shells. Which shell or shells are incomplete

1) L,M,N shells

2) M,N shells

3) N shells

4) K,L,M,N shells

Option 2 – M,N shells

There is no difference between valency and valence electrons except in case of

1) elements of group 2

2) elements of group 3

3) elements of group 4

4) elements of group 5

Option 4 – elements of group 5

Which of the following statements is wrong for the model of an atom as proposed by Rutherford

1) The atom consists of a positively charged centre called nucleus

2) Nucleus consists of protons and neutrons

3) Most of the mass is concentrated in the nucleus

4) The volume of nucleus is very small as compared to the total volume of the atom

Option 2 – Nucleus consists of protons and neutrons

Rutherford alpha- particle scattering experiment was responsible for the discovery of

1) Nucleus

2) neutron

3) mass number

4) atomic number

Option 1 – Nucleus

Mass number of an element can be obtained by adding

1) Number of electrons and neutrons

2) number of protons and neutrons

3) number if electrons and protons

4) number of electrons, protons and neutrons

Option 2 – number of protons and neutrons

If a neutral atom has three shells completely filled up, then the number electrons of the atom is

1) 28

2) 32

3) 30

4) 18

Option 3 – 30

Which one is not true for two isotopes?

1) Similar mass number

2) Similar atomic number

3) Similar chemical properties

4) Similar electronic configurations

Option 1 – Similar mass number

Calcium, Magnesium, Sulphur and Chlorine have atomic numbers 20, 12, 16, 17 respectively. Which of these does not show a valency of 2?

1) Calcium

2) Magnesium

3) Sulphur

4) Chlorine

Option 4 – Chlorine

The number of isotopes that are exhisted for both xenon and cesium are

1) 46

2) 16

3) 26

4) 36

Option 4 – 36

The isotope of iodine is used in the treatment of

1) cancer

2) goitre

3) age of fossil

4) fuel in nuclear react

Option 2 – goitre

Among the following which elements can show multiple valencies

1) sulphur

2) phosphorus

3) sodium

4) both a, b

Option 4 – both a, b

Isotopes have different physical properties due to

1) same number of protons

2) same number of electrons

3) same number of neutrons

4) Different number of neutrons or different mass numbers

Option 4 – Different number of neutrons or different mass numbers

An atom absorbs a UV photon of 200 nm and re-emits two photons. If the wavelength of one of the emitted photons is 700 nm. The wavelength of the second emitted photon will be ……….

(A) 900 nm

(B) 500 nm

(D) 7000 nm

Option c – 280 nm

In hydrogen atoms, if the radius of an orbit is made four times that of a smaller orbit, then the angular momentum of an electron becomes ……….. the angular momentum of an electron in a smaller orbit.

(A) twice

(B) half

(D) thrice

Option a – twice

Which one of the following has the least energy?

(A) n = 3, 1 = 2

(B) n=2, l=1

(D) n = 4, l=0

Option b – n=2, l=1

The mass of an electron is equal to the mass of a/an ……….

(A) alpha particle

(B) beta particle

(D) gamma rays

Option b – beta particle

Select the number of electrons that have n = 2 and s = +1/2.

(A) 3

(B) 4

(D) 9

Option b – 4

The orbital angular momentum of an electron depends on ………..

(A) only l

(B) only n and l

(D) only m and l

Option a – only l

The spectral line corresponding to the transition of an electron in the H-atom from the 4th orbit to the 3rd orbit is known as ………. series.

(A) Balmer

(B) Brackett

(D) Pfund

Option c – Paschen

Violet light can eject electrons from the surface of potassium metal but red light cannot because ……….

(A) the intensity of violet light is greater than red light and is enough to eject electrons

(B) the wavelength of violet light is greater than red light and is enough to eject electrons

(D) none of these

Option c – the frequency of red light is lower than violet light and is not enough to eject electrons

If the magnetic quantum number of an electron is represented by – 3, then which of the following can be its principal quantum number?

(A) 2

(B) 3

(D) 1

Option c – 4

An electron revolving around the nucleus behaves as a standing wave only when the circumference is equal to ………

(A) the radius of an orbit

(B) fractional multiple of the wavelength

(D) an integral multiple of the wavelength

Option d – an integral multiple of the wavelength

Which of the following is CORRECT for both cathode rays and anode rays?

(A) The particles of both rays travel in a straight line and in the same direction.

(B) In the presence of an electric field, both the rays deflect towards the negative electrode.

(D) The particles of both rays are electrically neutral.

Option c – Both rays are affected by a magnetic field.

The orbitals described by the following quantum numbers are ……….. respectively. (1) n = 5,1 = 3 (II) n = 6,1=0

(A) (I) = 5f; (II) = 6s

(B) (1)=5s; (II) = 6f

(D) (I) = 5f; (II) = 6p

Option a – (I) = 5f; (II) = 6s

For an electron in Bohr’s orbit, the energy difference between successive orbits in hydrogen atom when going away from the nucleus ………..

(A) increases

(B) remain unchanged

(D) first decreases and then increases

Option c – decreases

When an electron jumps from n = 3 to n = 1 in Bohr’s atom, the possible number of spectral lines is/are ………

(A) 4

(B) 2

(D) 3

Option d – 3

The orbitals, 2px and 2py differ in their ……..

(A) orientation

(B) shape

(D) size

Option a – orientation

The ionization energy of a hydrogen atom is ……..

(A) 13.6 eV

(B) 4.08 eV

(D) 2.72 eV

Option a – 13.6 eV

Bohr’s model can be applied to ……….

(A) elements containing more than one electron

(B) ions containing more than one electron

(D) only hydrogen atom

Option c – atoms or ions containing one electron

The ratio of the energies of photons of 3000 Å to that of 9000 Å is ……….

(A) 3 : 1

(B) 9 : 1

(D) 1 : 9

Option a – 3 : 1

The number of radial nodes for 4d orbital is ……..

(A) 1

(B) 2

(D) 4

Option a – 1

The charge-to-mass ratio of cathode ray particles obtained by using helium gas is ………. that of obtained by using hydrogen gas.

(A) greater than

(B) smaller than

(D) equal to

Option d – equal to

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