Structure of Atom

13 previous-year questions from this chapter every option and the correct answer, free · where the marks are

1. Bohr model and hydrogen spectrum

Exam focus: Bohr's energy and radius formulas are exact only for one-electron species (H, He⁺, Li²⁺) — applying them to a multi-electron atom without adjustment is the usual overreach. Only the Balmer series (transitions down to n=2) falls in the visible range; Lyman is UV and the rest are infrared.

Structure of Atom — Complete Chapter

Arjuna NEET

Full-chapter revision; Bohr's model and the hydrogen spectrum are covered within it alongside the rest of the chapter.

ChemistryNEET 2025show ▾

The ratio of the wavelengths of the light absorbed by a hydrogen atom when it undergoes the

n = 2 \to n = 3

and

n = 4 \to n = 6

transitions, respectively, is:

A. $\frac{1}{36}$
B. $\frac{1}{16}$
C. $\frac{1}{9}$
D. $\frac{1}{4}$ ✓

Solution

$\frac{1}{λ} \propto \frac{1}{n _{1}^{2}} - \frac{1}{n _{2}^{2}}$ . For $2 \to 3$ : $\frac{1}{4} - \frac{1}{9} = \frac{5}{36}$ . For $4 \to 6$ : $\frac{1}{16} - \frac{1}{36} = \frac{5}{144}$ . So $\frac{λ _{2 \to 3}}{λ _{4 \to 6}} = \frac{5/144}{5/36} = \frac{1}{4}$ .

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ChemistryNEET 2025show ▾

The energy and radius of the first Bohr orbit of

H e^{+}

and

L i^{2 +}

are (given

R_{H} = 2.18 \times 1 0^{- 18}

a_{0} = 52.9

pm):

A. $E (L i^{2 +}) = - 19.62 \times 1 0^{- 18}$ J, $r (L i^{2 +}) = 17.6$ pm; $E (H e^{+}) = - 8.72 \times 1 0^{- 18}$ J, $r (H e^{+}) = 26.4$ pm✓
B. $E (L i^{2 +}) = - 8.72 \times 1 0^{- 18}$ J, $r (L i^{2 +}) = 26.4$ pm; $E (H e^{+}) = - 19.62 \times 1 0^{- 18}$ J, $r (H e^{+}) = 17.6$ pm
C. $E (L i^{2 +}) = - 19.62 \times 1 0^{- 16}$ J, $r (L i^{2 +}) = 17.6$ pm; $E (H e^{+}) = - 8.72 \times 1 0^{- 16}$ J, $r (H e^{+}) = 26.4$ pm
D. $E (L i^{2 +}) = - 8.72 \times 1 0^{- 16}$ J, $r (L i^{2 +}) = 17.6$ pm; $E (H e^{+}) = - 19.62 \times 1 0^{- 16}$ J, $r (H e^{+}) = 17.6$ pm

Solution

$E_{n} = - R_{H} \frac{Z ^{2}}{n ^{2}}$ and $r_{n} = a_{0} \frac{n ^{2}}{Z}$ . $H e^{+}$ ( $Z = 2$ ): $E = - 4 \times 2.18 \times 1 0^{- 18} = - 8.72 \times 1 0^{- 18}$ J, $r = 52.9/2 = 26.4$ pm. $L i^{2 +}$ ( $Z = 3$ ): $E = - 9 \times 2.18 \times 1 0^{- 18} = - 19.62 \times 1 0^{- 18}$ J, $r = 52.9/3 = 17.6$ pm.

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ChemistryNEET 2024show ▾

The energy of an electron in the ground state (

n = 1

) of the

H e^{+}

ion is

- x

J. Then that of an electron in the

n = 2

state of the

B e^{3 +}

ion, in J, is:

A. $- \frac{x}{9}$
B. $- 4 x$
C. $- \frac{4 x}{9}$
D. $- x$ ✓

Solution

$E_{n} = - \frac{Z ^{2}}{n ^{2}} \times 13.6$ eV. For $H e^{+}$ ( $Z = 2$ , $n = 1$ ): factor $4$ . For $B e^{3 +}$ ( $Z = 4$ , $n = 2$ ): factor $\frac{16}{4} = 4$ . Same factor, so the energy is $- x$ J.

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ChemistryNEET 2022show ▾

If the radius of the second Bohr orbit of the

H e^{+}

ion is 105.8 pm, what is the radius of the third Bohr orbit of the

L i^{2 +}

ion?

A.158.7 Å
B.158.7 pm✓
C.15.87 pm
D.1.587 pm

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ChemistryNEET 2021show ▾

A particular station of All India Radio, New Delhi, broadcasts on a frequency of 1,368 kHz (kilohertz). The wavelength of the electromagnetic radiation emitted by the transmitter is (speed of light

c = 3.0 \times 1 0^{8} m s^{- 1}

A.219.3 m✓
B.219.2 m
C.2192 m
D.21.92 cm

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ChemistryNEET 2019show ▾

Which of the following series of transitions in the spectrum of the hydrogen atom falls in the visible region?

A.Lyman series
B.Balmer series✓
C.Paschen series
D.Brackett series

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2. Quantum numbers, orbitals and their shapes

Exam focus: Given a quantum number set, check l ≤ n−1 and |m| ≤ l first — that's where most "is this set possible" options actually fail. Total nodes equal n−1, split into l angular nodes and n−l−1 radial nodes, a formula NEET applies directly rather than just defining.

Structure of Atom — Complete Chapter

Arjuna NEET

Same full-chapter video; quantum numbers and orbital shapes are one section of this one-shot, not isolated.

ChemistryNEET 2024show ▾

Match List I with List II.

List I (Quantum number)	List II (Information provided)
A. $m_{l}$	I. Shape of orbital
B. $m_{s}$	II. Size of orbital
C. $l$	III. Orientation of orbital
D. $n$	IV. Orientation of spin of electron

Choose the correct answer from the options given below:

A.A-III, B-IV, C-I, D-II✓
B.A-III, B-IV, C-II, D-I
C.A-II, B-I, C-IV, D-III
D.A-I, B-III, C-II, D-IV

Solution

$n$ fixes orbital size (II), $l$ its shape (I), $m_{l}$ its orientation (III), and $m_{s}$ the spin orientation of the electron (IV). Hence A-III, B-IV, C-I, D-II.

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ChemistryNEET 2023show ▾

The relation between

n_{m}

(

n_{m}

= the number of permissible values of the magnetic quantum number

m

) for a given value of the azimuthal quantum number

l

is:

A. $l = \frac{n _{m} - 1}{2}$ ✓
B. $l = 2 n_{m} + 1$
C. $n_{m} = 2 l^{2} + 1$
D. $n_{m} = l + 2$

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ChemistryNEET 2022show ▾

Identify the incorrect statement from the following:

A.The shapes of $d_{x y}$ , $d_{y z}$ and $d_{z x}$ orbitals are similar to each other; and $d_{x^{2} - y^{2}}$ and $d_{z^{2}}$ are similar to each other✓
B.All the five 5d orbitals are different in size when compared to the respective 4d orbitals
C.All the five 4d orbitals have shapes similar to the respective 3d orbitals
D.In an atom, all the five 3d orbitals are equal in energy in the free state

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3. Electronic configuration, Aufbau, Pauli, Hund

Exam focus: Cr ([Ar]3d⁵4s¹) and Cu ([Ar]3d¹⁰4s¹) break the Aufbau filling order for the extra stability of a half-filled or filled d-subshell — NEET's standard exceptions. And when a transition metal ion forms, the 4s electrons are removed first, not 3d, even though 4s filled first — write Fe²⁺ with a 3d⁴4s² tail instead of the correct 3d⁶ and the trap has worked.

Structure of Atom — Complete Chapter

Arjuna NEET

Same full-chapter video; Aufbau/Pauli/Hund's-rule electronic configuration is covered as part of the chapter, not standalone.

1. Bohr model and hydrogen spectrum

Bohr's model and the hydrogen spectrum

2. Quantum numbers, orbitals and their shapes

Quantum numbers, orbitals and their shapes

3. Electronic configuration, Aufbau, Pauli, Hund

Electronic configuration: Aufbau, Pauli and Hund