BoardChemistry

Structure of Atom

29 Board Chemistry previous year questions on Structure of Atom — options free on every question; 3 include the answer & explanation free, the rest unlock with PYQ Pass.

Q1 FREE PREVIEW
PYQ

In a multielectron atom, which of the following orbitals described by three quantum numbers will have same energy in absence of electric and magnetic fields?
A. \(n=1,1=0,{m}_{1}=0\)
B. \(n=2,1=0,{m}_{1}=0\)
C. \(n=2,1=1,{m}_{1}=1\)
D. \(n=3,1=2,{m}_{1}=1\)
E. \(n=3,1=2,{m}_{1}=0\)

Choose the correct answer from the options given below:

[JEE Main 2025, 28 Jan (Shift 1)]

a

A and B Only

b

D and E Only

c

B and C Only

d

C and D Only

✓ Correct answer: b)

D and E Only

Explanation

In a multi-electron atom, the orbitals (D) n = 3, l = 2, m = 1 and (E) n = 3, l = 2, m = 0 described by the three quantum numbers will have the same energy in the absence of magnetic and electric fields.

D and E are 3d orbital.

Q2 FREE PREVIEW
PYQ

For hydrogen atom, the orbital/s with lowest energy is/are :
(A) 4 s
(B) \(3{p}_{x}\)
(C) \(3{d}_{{x}^{2}-{y}^{2}}\)
(D) \(3{d}_{{z}^{2}}\)
(E) \(4{p}_{z}\)

Choose the correct answer from the options given below :

a

(A) and (E) only

b

(B), (C) and (D) only

c

(B) only

d

(A) only

✓ Correct answer: b)

(B), (C) and (D) only

Explanation

For H-atoms, orbitals in the shell are degenerate, meaning energy depends only on the value of ' n '.

\(∴{E}_{3{p}_{x}}={E}_{3{d}_{{x}^{2}-{y}^{2}}}={E}_{3{d}_{{z}^{2}}}\)

Q3 FREE PREVIEW
PYQ

The four quantum numbers for the electron in the outer most orbital of potassium (atomic no. 19) are

a

\(\mathrm{n}=4,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2\)

b

\(\mathrm{n}=2,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2\)

c

\(\mathrm{n}=3,\mathrm{l}=2,\mathrm{m}=−1,\mathrm{s}=+1/2\)

d

\(\mathrm{n}=3,\mathrm{l}=0,\mathrm{m}=1,\mathrm{s}=+1/2\)

✓ Correct answer: a)

\(\mathrm{n}=4,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2\)

Explanation

Step-by-step Short Solution:
- Potassium (Z = 19)

Electron configuration:

\[1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^1\]

  • The outermost electron is in the 4 s orbital, so:
  • Principal quantum number \(n=4\)
  • Azimuthal quantum number \(l=0\) (since it's an 's' orbital)
  • Magnetic quantum number \(m=0\) (only one value for \(l=0\) )
  • Spin quantum number \(s=+\frac{1}{2}\) (assumed to be \(+1 / 2\) for the first electron)

Final Answer:
A) \(n=4, l=0, m=0, s=+\frac{1}{2}\)

Q4
PYQ

Consider the ground state of chromium atom (Z = 24). How many electrons are with Azimuthal quantum number l = 1 and l = 2 respectively ?

[JEE Main 2025, 4 Apr (Shift 2)]

a

12 and 4

b

16 and 4

c

12 and 5

d

16 and 5

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Q5
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Bohr's model is applicable for a single electron atom of atomic number Z. Dependency of frequency of rotation of electron in \({\mathrm{n}}^{\mathrm{th}}\) principal quantum number is proportional to (Memory Based Question 28/Jan/25 Evening shift)

a

\(\frac{\mathrm{Z}}{{\mathrm{n}}^{2}}\)

b

\(\frac{{\mathrm{Z}}^{2}}{{\mathrm{n}}^{3}}\)

c

\(\frac{{\mathrm{n}}^{3}}{\mathrm{z}}\)

d

\(\frac{\mathrm{Z}}{\mathrm{n}}\)

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Q6
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A photon of wavelength 3000 \(\overset{^\circ }{\mathrm{A}}\) strikes a metal surface. The work function of the metal is 2.13 eV. What is the kinetic energy of the emitted photoelectron?
(h = 6.626 × \({10}^{-34}\) Js)

a

4.0 eV

b

3.0 eV

c

2.0 eV

d

1.0 eV

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Q7
PYQ

If radius of the first Bohr orbit of H-atom is \({\mathrm{a}}_{\mathrm{o}}\), then find the radius of 2nd Bohr's orbit of H-atom (memory based jee mains shift-1 29/01/2025)

a

\(8{\mathrm{a}}_{\mathrm{o}}\)

b

\(4{\mathrm{a}}_{\mathrm{o}}\)

c

\(2{\mathrm{a}}_{\mathrm{o}}\)

d

\(6{a}_{\mathrm{o}}\)

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Q8
PYQ

The extra stability of half-filled subshell is due to
(A) Symmetrical distribution of electrons
(B) Smaller coulombic repulsion energy
(C) The presence of electrons with the same spin in non-degenerate orbitals
(D) Larger exchange energy
(E) Relatively smaller shielding of electrons by one another
Identify the correct statements

[JEE Main 2025, 7 Apr (Shift 2)]

a

(B), (D) and (E) only

b

(A), (B), (D) and (E) only

c

(B), (C) and (D) only

d

(A), (B) and (D) only

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Q9
PYQ

An electron of \({\mathrm{He}}^{+}\) is present in 3rd excited state. Find its De-broglie wavelength.

a

\(6.64\overset{\mathrm{o}}{\mathrm{A}}\)

b

\(1.66\overset{\mathrm{o}}{\mathrm{A}}\)

c

\(3.32\overset{\mathrm{o}}{\mathrm{A}}\)

d

\(13.28\overset{\mathrm{o}}{\mathrm{A}}\)

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Q10
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Given below are two statements :
Statement (I): It is impossible to specify simultaneously with arbitrary precision, both the linear momentum and the position of a particle.
Statement (II): If the uncertainty in the measurement of position and uncertainty in measurement of momentum are equal for an electron, then the uncertainty in the measurement of velocity is \(⩾\sqrt{\frac{h}{\pi }}\times \frac{1}{2m}\).
In the light of the above statements, choose the correct answer from the options given below :

a

Both Statement I and Statement II are true

b

Statement I is false but Statement II is true

c

Statement I is true but Statement II is false

d

Both Statement I and Statement II are false

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Q11
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Correct statements for an element with atomic number 9 are
(i). There can be 5 electrons for which \({\mathrm{m}}_{\mathrm{s}}=+\frac{1}{2}\) and 4 electrons for which \({\mathrm{m}}_{\mathrm{s}}=-\frac{1}{2}\)
(ii). There is only one electron in \({p}_{z}\)orbital
(iii). The last electron goes to orbital with \(\mathrm{n}=2\) and \(l=1\)
(iv). The sum of angular nodes of all the atomic orbitals is 1 .


Choose the correct answer from the options given below:

a

(iii) and (iv) only

b

(i) and (iii) only

c

(i), (iii) and (iv) only

d

(i) and (ii) only

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Q12
PYQ

Radius of the first excited state of Helium ion is given as : \({a}_{0}\to\) radius of first stationary state of hydrogen atom

[JEE Main 2025, 22 Jan (Shift 1)]

a

\(r=2{a}_{0}\)

b

\(r=4{a}_{0}\)

c

\(r=\frac{{a}_{0}}{2}\)

d

\(r=\frac{{a}_{0}}{4}\)

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Q13
PYQ

Consider the following statements :
(A) The principal quantum number ‘n’ is a positive integer with values of ‘n’ = 1, 2, 3, …
(B) The azimuthal quantum number ‘l’ for a given ‘n’ (principal quantum number) can have values as ‘l’ = 0, 1, 2, … n
(C) Magnetic orbital quantum number ‘ml ’for a particular ‘l’ (azimuthal quantum number) has (2l + 1)values.
(D) ±1/ 2 are the two possible orientations of electron spin.
(E) For l = 5,there will be a total of 9 orbital
Which of the above statements are correct ?

a

(A), (B) and (C)

b

(A), (C), (D) and (E)

c

(A), (C) and (D)

d

(A), (B), (C) and (D)

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Q14
PYQ

Radius of electron in ground state for hydrogen is \({a}_{o}\), then radius of electron in \({\mathrm{He}}^{+}\)ion in \({3}^{\mathrm{rd}}\) excited state is a. Then \(\frac{{\mathrm{a}}_{\mathrm{o}}}{\mathrm{a}}\) is:

(Memory Based JEE Mains 22/01/2025,Shift -1)

a

1/2

b

1/4

c

1/16

d

1/8

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Q15
PYQ

Radius of electron in ground state for hydrogen is \({a}_{o}\), then radius of electron in \({\mathrm{He}}^{+}\)ion in \({3}^{\mathrm{rd}}\) excited state is a. Then \(\frac{{\mathrm{a}}_{\mathrm{o}}}{\mathrm{a}}\) is:

(Memory Based JEE Mains 22/01/2025,Shift -1)

a

1/2

b

1/4

c

1/16

d

1/8

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Q16
PYQ

If \({a}_{0}\) is denoted as the Bohr radius of hydrogen atom, then what is the de-Broglie wavelength \((\lambda )\) of the electron present in the second orbit of hydrogen atom? [n : any integer]

[JEE Main 2025, 29 Jan (Shift 1)]

a

\(\frac{2{a}_{0}}{n\pi }\)

b

\(\frac{4\pi {a}_{0}}{n}\)

c

\(\frac{8\pi {a}_{0}}{n}\)

d

\(\frac{4n}{\pi {a}_{0}}\)

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Q17
PYQ

The four quantum numbers for the electron in the outer most orbital of potassium (atomic no. 19) are

a

\(\mathrm{n}=4,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2\)

b

\(\mathrm{n}=2,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2\)

c

\(\mathrm{n}=3,\mathrm{l}=2,\mathrm{m}=−1,\mathrm{s}=+1/2\)

d

\(\mathrm{n}=3,\mathrm{l}=0,\mathrm{m}=1,\mathrm{s}=+1/2\)

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Q18
PYQ

The correct order of energy of the following subshell is

1s, 2s, 3p, 3d

(Memory Based Question 28/Jan/25 Evening shift)

a

1s < 2s < 3d < 3p

b

2s < 1s < 3p < 3d

c

1s < 3p < 2s < 3d

d

1s < 2s < 3p < 3d

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Q19
PYQ

The energy of an electron in the ground state (n = 1) for \({\mathrm{He}}^{+}\) ion is \(-\mathrm{x}\) Joules then that for an electron in n = 2 state for \({\mathrm{Be}}^{3+}\)ion in Joule is

a

\(-\frac{4}{9}\mathrm{x}\)

b

\(-\mathrm{x}\)

c

\(-\frac{\mathrm{x}}{9}\)

d

\(-4\mathrm{x}\)

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Q20
PYQ

According to Bohr's model, the highest kinetic energy is associated with the electron in the:

a

first orbit of \(\mathrm{H}\) atom.

b

first orbit of \({\mathrm{He}}^{+}\).

c

second orbit of \({\mathrm{He}}^{+}\).

d

second orbit of \({\mathrm{Li}}^{2+}\).

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Q21
PYQ

Heat treatment of muscular pain involves radiation of a wavelength of about 900 nm. Which spectral line of the H atom is suitable for this?

(Rydberg constant \({\mathrm{R}}_{\mathrm{H}}={10}^{5}{\mathrm{cm}}^{-1},\mathrm{h}=6.6\times {10}^{-34}\mathrm{Js},\mathrm{c}=3\times {10}^{8}\mathrm{m}/\mathrm{s}\))

[JEE Main 2025, 23 Jan (Shift 1)]

a

Lyman series,\(\infty \to 1\)

b

Balmer series,\(\infty \to 2\)

c

Paschen series, \(5\to 3\)

d

Paschen series, \(\infty \to 3\)

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Q22
PYQ

The correct set of four quantum numbers for the valence electron of rubidium atom \((\mathrm{Z}=37)\) is :

a

\(5,0,0,+\frac{1}{2}\)

b

\(5,1,1,+\frac{1}{2}\)

c

\(5,0,1,+\frac{1}{2}\)

d

\(5,1,0,+\frac{1}{2}\)

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Q23
PYQ

The quantum numbers of four electrons are given below

I. \(n=4 ; l=2 ; m_l=-2 ; s=-\frac{1}{2}\)
II. \(n=3 ; l=2 ; m_l=1 ; s=+\frac{1}{2}\)
III. \(n=4 ; l=1 ; m_l=0 ; s=+\frac{1}{2}\)
IV. \(n=3 ; l=1 ; m_l=-1 ; s=+\frac{1}{2}\)

The correct decreasing order of energy of these electrons is

[Re-NEET 2024]

a

IV \(>\) II \(>\) III \(>\) I

b

I \(>\) III \(>\) II \(>\) IV

c

III \(>\) I \(>\) II \(>\) IV

d

I \(>\) II \(>\) III \(>\) IV

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Q24
PYQ

Which of the following energy order is correct for H-atoms?

Memory Based Question 28/Jan/25 Evening shift

a

1s < 2s < 2p < 3s

b

1s < 2s = 2p < 3s = 3p

c

1s < 2s < 3s <4s

d

1s < 2s < 2p < 3p < 3s

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Q25
PYQ

If the de-Broglie wavelength of a particle of mass (m) is 100 times its velocity,

then its value in terms of its mass (m) and Planck constant (h) is:

a

\(\overset{1}{\underset{10}{-}}\sqrt{\frac{m}{h}}\)

b

\(10\sqrt{\frac{h}{m}}\)

c

\(\overset{1}{\underset{10}{-}}\sqrt{\frac{h}{m}}\)

d

\(10\sqrt{\frac{m}{h}}\)

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Q26
PYQ

Which of the following is/are not correct with respect to energy of atomic orbitals of hydrogen atom?
(A) 1s < 2p < 3d < 4s
(B) \(1s<2s=2p<3s=3p\)
(C) 1s < 2s < 2p < 3s < 3p
(D) \(1s<2s<4s<3d\)

Choose the correct answer from the options given below :

a

(A) and (C) only

b

(A) and (B) only

c

(B) and (D) only

d

(C) and (D) only

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Q27
PYQ

Given below are two statements :

Statement (I) : A spectral line will be observed for a 2px → 2py transition.

Statement (II) : \(2{\mathrm{p}}_{\mathrm{x}}\mathrm{and}2{\mathrm{p}}_{\mathrm{y}}\)are degenerate orbitals.

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

a

Both Statement I and Statement II are true

b

Statement I is false but Statement II is true

c

Statement I is true but Statement II is false

d

Both Statement I and Statement II are false

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Q28
PYQ

If radius of the first Bohr orbit of H-atom is \({\mathrm{a}}_{\mathrm{o}}\), then find the radius of 2nd Bohr's orbit of H-atom (memory based jee mains shift-1 29/01/2025)

a

\(8{\mathrm{a}}_{\mathrm{o}}\)

b

\(4{\mathrm{a}}_{\mathrm{o}}\)

c

\(2{\mathrm{a}}_{\mathrm{o}}\)

d

\(6{a}_{\mathrm{o}}\)

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Q29
PYQ

Which of the following has the same energy in the absence of electric and magnetic field for the hydrogen atom? (Memory-based Question 28/ Jan/25 morning shift )

a

2s,3p

b

3s, 2p

c

2s, 2p

d

3s, 4f

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