Structure of Atom JEE Main Questions 2025: Important Practice Questions with PYQs

1.

The electrons identified by quantum numbers n and l

a) n = 4, / = 1 b) n = 4, l = 0

c) n = 3, l = 2 d) n = 3, / = 1

can be placed in order of increasing energy as

l)c<d<b<a 2)d<b<c<a

3)b<d<a<a 4)a<c<b<d

(2) Greater the (n + /) value, greater is the energy. If (n + l) values are equal, then the greater the ‘n’ value greater is the energy.

2.

Which of the following sets of quantum numbers represents the highest energy of an atom?

(1)n=3, 1=2, m=l, s=+l/2

(2)n=3, 1=2, m=l, s=+l/2

(3)n=4, 1=0, m=0, s=+l/2

(4)n=3, 1=0, m=0, s= +1/2

(2) Maximum value of (n +1) denotes the high­est energy of the orbital.

3.

Which of the following statements in relation to the hydrogen atom is correct?

(1)3s orbital is lower in energy than 3p orbital

(2)3p orbital is lower in energy than 3d orbital

(3)3s and 3p orbitals are of lower energy than 3d orbital

(4)3s, 3p and 3d orbitals all have the same energy

4) Auf-bau principle is not applicable for H atom

4.

In a multi-electron atom, which of the following orbitals described by the three quantum numbers will have the same energy in the absence of magnetic and electric fields?(2005)

(a) n = 1,1 = 0, m = 0 (b) n = 2,1 = 0, m = 0

(c) n = 2,1 = 1, m = 1 (d) n = 3,1 = 2, m = 1 (e) n = 3,1 = 2, m = 0

1) (a) and (b) 2) (b) and (c)

3) (c) and (d) 4) (d) and (e)

(4) n is same and orbital is 3d.

5.

Which of the following ions has the maximum magnetic moment?
1) Mn+2 2) Fe+2 3) Ti+2 4) Cr+2

(1) Mn2+ has the maximum number of unpaired electrons (5) and therefore has maximum moment

6.

The incorrect postulates of the Dalton's atomic theory are :

(A) Atoms of different elements differ in mass.

(B) Matter consists of divisible atoms.

(C) Compounds are formed when atoms of different elements combine in a fixed ratio.

(D) All the atoms of given element have different properties including mass.

(E) Chemical reactions involve the reorganization of atoms.

Choose the correct answer from the options given below :

1. B D
2. A B D
3. B D E
4. C D E

Matter consists of non-divisible atoms.

All the atoms of given element have same properties including mass.

Hence, statements (B) and (D) are incorrect.

7.

Given below are two statements.

Statement I : According to Bohr's model of an atom, qualitatively the magnitude of velocity of electron increases with decrease in positive charges on the nucleus as there is no strong hold on the electron by the nucleus.

Statement II : According to Bohr's model of an atom, qualitatively the magnitude of velocity of an electron increases with decrease in principal quantum number.

In the light of the above statements, choose the most appropriate answer from the options given below :

1. Both statements I and II are false
2. Both statements I and II are true
3. Statement I is false but statement II is true
4. Statement I is true but statement II is false

C is correct

8.

Given below are two statements :

Statement I: Rutherford's gold foil experiment cannot explain the line spectrum of hydrogen atom.

Statement II: Bohr's model of hydrogen atom contradicts Heisenberg' uncertainty principle.

In the light of the above statements, choose the most appropriate answer from the options given below :

1. Statement I is false but statement II is true
2. Statement I is true but statement II is false
3. Both statements I and II are false
4. Both statements I and II are true

D is correct

Rutherford's gold foil experiment only proved that electrons are held towards the nucleus by electrostatic forces of attraction and move in circular orbits with very high speeds.

Bohr's model gave exact formula for the simultaneous calculation of speed & distance of electron from the nucleus, something which was deemed impossible according to Heisenberg.

9.

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R :

Assertion A: In the photoelectric effect, the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface.

Reason R: When the photon of any energy strikes an electron in the atom, transfer of energy from the photon to the electron takes place.

In the light of the above statements, choose the most appropriate answer from the options given below :

• Both A and R are correct and R is the correct explanation of A
• A is not correct but R is correct
• A is correct but R is not correct
• Both A and R are correct and R is not the correct explanation of A

Given are two statements :

• Assertion A : "In the photoelectric effect, the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface."
• Reason R : "When the photon of any energy strikes an electron in the atom, transfer of energy from the photon to the electron takes place."

From the understanding of the photoelectric effect, we know that the light beam must have a frequency v that is greater than the threshold frequency v0 for electrons to be ejected from the metal surface. Therefore, Assertion A is correct. However, Reason R is somewhat misleading in the context of the photoelectric effect. It's true that a photon transfers its energy to an electron when it strikes the electron. However, for the electron to be ejected (i.e., the photoelectric effect to occur), the energy of the photon, given by Ephoton=h⋅v, where h is Planck's constant and v is the frequency of the light, must be greater than the work function (the minimum energy needed to eject an electron) of the metal. This condition is not captured in Reason R.

Therefore, the correct answer is :

Option C: Assertion A is correct, but Reason R is not correct.

10.

Given below are two statements :

Statement (I): The orbitals having the same energy are called degenerate orbitals.

Statement (II): In hydrogen atom, 3p and 3d orbitals are not degenerate orbitals.

In the light of the above statements, choose the most appropriate answer from the options given below :

1. Statement I is true but Statement II is false
2. Statement I is false but Statement II is true
3. Both Statements I and II are false
4. Both Statements I and II are true

For single electron species the energy depends upon the principal quantum number 'n only. So, statement II is false.

Statement I is the correct definition of degenerate orbitals.

11.

The number of radial and angular nodes in 4d orbital are, respectively

1. 1 and 2
2. 3 and 2
3. 1 and 0
4. 2 and 1

We know,

Radial nodes = n − l − 1

and Angular nodes = l

For 4d orbital,

n = 4

l = 2

∴ Radial nodes = 4 − 2 − 1 = 1

Angular nodes = 2

12.

Which of the following statements is correct?

(A) The electronic configuration of Cr is [Ar] 3d5 4s1.

(B) The magnetic quantum number may have a negative value.

(C) In the ground state of an atom, the orbitals are filled in order of their increasing energies.

(D) The total number of nodes are given by n −

Choose the most appropriate answer from the options given below :

1. A C D
2. A B
3. A C
4. A B C

(A) Cr (24) = 1s2 2s2 2p6 3s2 3p6 3d5 4s1

= [Ar] 3d5 4s1

(B) Magnetic quantum number (m) values ranging from − l to + l including zero.

∴ It can have negative value.

(C) According to Aufbau rule, electrons are filled first in these orbitals which have low energy.

∴ Statement C is correct.

(D) We know,

Number of Radial nodes = n − l −1

and number of Angular nodes = l

∴ Total nodes = n − l − 1 + 1 = n − 1

13.

Given below are two statements: One is labelled as Assertion

A

and the other is labelled as Reason

R

Assertion

A

: Zero orbital overlap is an out-of-phase overlap.

Reason

R

: It results due to different orientations/directions ofthe  approach of orbitals.

In the light of the above statements, choose the correct answer from the options given below

• Both A and R are correct and R is the correct explanation of A
• Both A and R are correct and R is not the correct explanation of A
• A is true but R is false
• A is false but R is true

A is correct. Zero overlapping is something in which there is no overlapping between two orbitals. The first condition is that the two orbitals should not be symmetrical and the second condition is that both orbitals should be in different planes.

14.

The number of s-electrons present in an ion with 55 protons in its unipositive state is

1. 10
2. 9
3. 12
4. 8

The number of protons in an element determines its atomic number, which is the number of electrons in a neutral atom of the element. The unipositive state of an ion indicates that it has lost one electron. Therefore, the number of electrons in a unipositive ion is one less than the atomic number.

The element with 55 protons is cesium (Cs), which is in group 1 of the periodic table. Group 1 elements have one valence electron in the s sublevel of their outermost energy level.

In a neutral atom of caesium, there are 55 electrons, with the electron configuration [Xe] 6s1. When cesium loses one electron to form a unipositive ion (Cs+), the resulting ion has 54 electrons.

Out of these 54 electrons s subshell has 10 electrons in 1s2, 2s2, 3s2, 4s2, 5s2.

15.

The orbital having two radial as well as two angular nodes is :

1. 3p
2. 5d
3. 4d
4. 4f

Number of radial nodes = (n – l – 1)

Number of angular nodes = l

for 5d; n = 5, l = 2

5d orbital has two radial nodes and two angular nodes