NEET PhysicsUpdated 19 Oct 2026

Atoms: NEET PYQs and weightage

Atoms carries 3.0 of 100 Physics marks in NEET by past-paper share: 23 of the 758 tagged NEET Physics PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 15 of 30 Physics chapters.

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3.0/100 Weight in Physics

Exam importance (3/5, by past-paper share)

23 NEET PYQs

191 Practice questions

174 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Physics PYQs in the bank (23 of 758), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Atoms: formula sheet for NEET

13 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Energy of nth level (hydrogen)
$E_{n} = - \frac{m e ^{4}}{8 ε _{0}^{2} h ^{2} n ^{2}} = - \frac{13.6 eV}{n ^{2}}$
Use it when: you need the energy of any Bohr level; $n = 1$ gives the ground state, $- 13.6 eV$
Photon in a jump
$h ν = E_{i} - E_{f} (emission, E_{i} > E_{f})$
$E_{i} + h ν = E_{f} (absorption)$
Use it when: you need the frequency or wavelength of light emitted or absorbed between two levels
Bohr quantisation
$L = m v r = \frac{nh}{2 π} (n = 1, 2, 3, \dots)$
Use it when: a question gives $n$ and asks for angular momentum, or wants $v$ from $r$
Radius of nth orbit
$r_{n} = \frac{ε _{0} n ^{2} h ^{2}}{π m e ^{2}} = n^{2} \times 5.3 \times 1 0^{- 11} m$
Use it when: you compare orbit sizes; $r$ grows as $n^{2}$ , so $r_{2} = 4 r_{1}$ and $r_{3} = 9 r_{1}$
Energies in an orbit of radius r
$K = \frac{e ^{2}}{8 π ε _{0} r}$
$U = - \frac{e ^{2}}{4 π ε _{0} r}$
$E = K + U = - \frac{e ^{2}}{8 π ε _{0} r}$
Use it when: a question asks for the kinetic, potential or total energy of the electron
Quick link
$K = - E$
$U = 2 E$
Use it when: $E$ is given (ground state $- 13.6 eV$ ) and you want $K$ and $U$ straight away: $K = + 13.6 eV$ , $U = - 27.2 eV$
Ionisation energy
$13.6 eV (from the ground state)$
$\frac{13.6}{n ^{2}} eV (from level n; free electron at rest has E = 0)$
Use it when: a question asks for the minimum energy to free the electron from a given level
Key level values
$E_{2} = - 3.40 eV$
$E_{3} = - 1.51 eV$
$1 \to 2 : 10.2 eV$
$1 \to 3 : 12.09 eV$
Use it when: an electron beam or photon of given energy hits ground-state hydrogen and you must find which levels it can reach
Distance of closest approach (α-particle, head-on)
$d = \frac{2 Z e ^{2}}{4 π ε _{0} K}$
Use it when: an $α$ -particle of kinetic energy $K$ stops momentarily near a nucleus; put $K$ in joules ( $1 eV = 1.6 \times 1 0^{- 19} J$ )
Coulomb force on an α-particle
$F = \frac{1}{4 π ε _{0}} \frac{( 2 e ) ( Z e )}{r ^{2}}$
Use it when: you need the repulsion between an $α$ -particle (charge $2 e$ ) and a nucleus (charge $Z e$ ) at distance $r$
Orbit condition
$\frac{m v ^{2}}{r} = \frac{e ^{2}}{4 π ε _{0} r ^{2}}$
$r = \frac{e ^{2}}{4 π ε _{0} m v ^{2}}$
$v = \frac{e}{4 π ε _{0} m r}$
Use it when: you know $r$ and need $v$ , or the other way round
de Broglie picture of orbits
$2 π r_{n} = nλ$
$λ = \frac{h}{m v}$
Use it when: a question asks how many electron wavelengths fit in the $n$ th orbit (answer: $n$ )
Revolution frequency
$ν = \frac{v}{2 π r}$
$T = \frac{2 π r}{v}$
Use it when: you need how often the electron goes round its orbit; this is not the frequency of the emitted light

Trap

Bohr energies are negative. Exciting hydrogen from n = 1 to n = 2 needs E₂ − E₁ = 10.2 eV, not 3.4 eV. In the same way, the electron's kinetic energy is +13.6 eV even though its total energy is −13.6 eV.

How does NEET ask Atoms?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1PhysicsNEET UG PYQAtomic Spectra

Try right here · No sign-in

In hydrogen spectrum, the shortest wavelength in the Balmer series is

λ

. The shortest wavelength in the Bracket series is:

Answer key (A) & worked solution

Correct answer: Option A

Shortest wavelength in Balmer series when transition of

\overset{e}{ˉ}

from

\infty

n = 2

∵ \frac{1}{λ} = R z^{2} [\frac{1}{2 ^{2}} - \frac{1}{\infty ^{2}}]

\frac{1}{λ} = \frac{R}{4} .... (1)

Shortest wavelength is Bracket series when transition of

\overset{e}{ˉ}

from

\infty

n = 4

\frac{1}{λ ^{'}}^{'} = R (1)^{2} [\frac{1}{4 ^{2}} - \frac{1}{\infty ^{2}}] \Rightarrow \frac{1}{λ ^{'}}^{'} = \frac{R}{16} .... (2)

Eq. (1) / Eq. (2)

\frac{λ ^{'}}{λ} = \frac{R}{4} \times \frac{16}{R} \Rightarrow λ^{'} = 4 λ

Q2PhysicsNEET UG PYQBohr Model of the Hydrogen Atom

In the first excited state of hydrogen atom, the energy of its electron is -3.4 eV . The radial distance of the electron from the hydrogen nucleus in this case is approximately: (Take

1 eV = 1.6 \times 1 0^{- 19} J, e = 1.6 \times 1 0^{- 19} C

and

\frac{1}{4 π ε _{0}} = 9 \times 1 0^{9} N m^{2} / C^{2}

)

2.1 \times 1 0^{- 8} m

2.1 \times 1 0^{- 11} m

2.1 \times 1 0^{- 9} m

2.1 \times 1 0^{- 10} m

Answer key (D) & worked solution

Correct answer: Option D

\frac{K Q ^{2}}{2 r} = 3.4 eV

\frac{9 \times 1 0 ^{9} \times ( 1.6 \times 1 0 ^{- 19} ) ^{2}}{2 \times 3.4 \times 1.6 \times 1 0 ^{- 19}} = r 2.1176 \times 1 0^{- 10} = r r = 2.1 \times 1 0^{- 10} m

Q3PhysicsNEET UG PYQAtomic Spectra

Given the value of Rydberg constant is 10

^{7}

^{- 1}

, the wave number of the last line of the Balmer series in hydrogen spectrum will be

A0.025 × 10

^{4}

m−1

B0.5 × 10

^{7}

m−1

C0.25 × 10

^{7}

m−1

D2.5 × 10

^{7}

m−1

Answer key (C) & worked solution

Correct answer: Option C

\frac{1}{λ} = R Z^{2} (\frac{1}{n _{2}^{2}} - \frac{1}{n _{1}^{2}}) = 1 0^{7} \times 1^{2} (\frac{1}{2 ^{2}} - \frac{1}{\infty ^{2}})

⇒ wave number

= \frac{1}{λ} = 0.25 \times 1 0^{7} m^{- 1}

Q4PhysicsNEET UG PYQBohr Model of the Hydrogen Atom

The radius of inner most orbit of hydrogen atom is

5.3 \times 1 0^{- 11} m

. What is the radius of third allowed orbit of hydrogen atom?

A1.06 Å

B1.59 Å

C4.77 Å

D0.53 Å

Answer key (C) & worked solution

Correct answer: Option C

Radius of n

^{t h}

orbit in Hydrogen Atom

r_{n} = 0.53 \times \frac{n ^{2}}{Z}

Å So, radius of third orbit

r_{3} = 0.53 \times \frac{( 3 ) ^{2}}{( 1 )}

Å = 4.77 Å

Q5PhysicsNEET UG PYQBohr Model of the Hydrogen Atom

Let T

_{1}

and T

_{2}

be the energy of an electron in the first and second excited states of hydrogen atom, respectively. According to the Bohr’s model of an atom; the ratio T

_{1}

: T

_{2}

is:

A1 : 4

B4 : 1

C4 : 9

D9 : 4

Answer key (D) & worked solution

Correct answer: Option D

E_{n} = - 13.6 \frac{z ^{2}}{n ^{2}}

_{1}

= E

_{2}

(First excited state = n = 2)

\frac{T _{1}}{T _{2}} = \frac{E _{2}}{E _{3}} = \frac{3 ^{2}}{2 ^{2}} = \frac{9}{4}

_{2}

= E

_{3}

(Second excited state = n = 3)

Q6PhysicsNEET UG PYQAtomic Spectra

Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is

A5:27

B3:23

C7:29

D9:31

Answer key (A) & worked solution

Correct answer: Option A

Rydberg formula is given as

\frac{1}{λ} = R (\frac{l}{( n ^{'} ) ^{2}} - \frac{1}{n ^{2}})

For Lyman series

\frac{1}{λ} = R (\frac{l}{1 ^{2}} - \frac{1}{2 ^{2}})

\frac{1}{λ} = \frac{3 R}{4}

∴ λ = \frac{4}{3 R}

…………[equation 1] For Balmer series,

∴ \frac{1}{λ _{b}} = R (\frac{l}{2 ^{2}} - \frac{1}{3 ^{2}})

\frac{1}{λ _{b}} = \frac{5 R}{36}

∴ λ_{b} = \frac{36}{5 R}

……………[equation 2]

\frac{λ}{λ _{b}} = \frac{4}{3 R} \times \frac{5 R}{36}

∴ \frac{λ}{λ _{b}} = \frac{5}{27}

Q7PhysicsNEET UG PYQBohr Model of the Hydrogen Atom

If an electron in a hydrogen atom jumps from the 3

^{r d}

orbit to the 2

^{n d}

orbit, it emits a photon of wavelength λ. When it jumps from the 4

^{t h}

orbit to the 3

^{r d}

orbit, the corresponding wavelength of the photon will be

\frac{9}{16} λ

\frac{20}{7} λ

\frac{20}{13} λ

\frac{16}{25} λ

Answer key (B) & worked solution

Correct answer: Option B

Transition : 3 → 2 ⇒ Wavelength λ Transition : 4 → 3 ⇒ Wavelength λ'=?

\frac{\frac{1}{λ}}{\frac{1}{λ ^{'}}} = \frac{R _{H} Z ^{2} ( \frac{1}{2 ^{2}} - \frac{1}{3 ^{2}} )}{R _{H} Z ^{2} ( \frac{1}{3 ^{2}} - \frac{1}{4 ^{2}} )} \Rightarrow \frac{λ ^{'}}{λ} = \frac{20}{7} \Rightarrow λ^{'} = \frac{20 λ}{7}

Q8PhysicsNEET UG PYQBohr Model of the Hydrogen Atom

The total energy of an electron in an atom in an orbit is – 3.4 eV. Its kinetic and potential energies are, respectively:

A− 3.4 eV, − 6.8 eV

B3.4 eV, − 6.8 eV

C3.4 eV, 3.4 eV

D− 3.4 eV, − 3.4 eV

Answer key (B) & worked solution

Correct answer: Option B

In Bohr's model of H atom

∴ K . E = ∣ T E ∣ = \frac{∣ U ∣}{2} ∴ K . E . = 3.4 e V U = - 6.8 e V

Which topics in Atoms carry the most questions?

All 4 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Bohr Model of the Hydrogen Atom	12	101
Atomic Spectra	8	72
Alpha-Particle Scattering and Rutherford's Nuclear Model of Atom	2	17
Miscellaneous Examples	1	1

Why does Atoms show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Atoms, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Atoms?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Atoms test

Chapters either side of Atoms by weight

Wave Optics Weight 3.4/100 Units and Measurement Weight 3.2/100 Oscillations Weight 3.0/100 Mechanical Properties of Fluids Weight 2.9/100

Atoms: NEET PYQs and weightage

Atoms: formula sheet for NEET

Energy of nth level (hydrogen)

Photon in a jump

Bohr quantisation

Radius of nth orbit

Energies in an orbit of radius r

Quick link

Ionisation energy

Key level values

Distance of closest approach (α-particle, head-on)

Coulomb force on an α-particle

Orbit condition

de Broglie picture of orbits

Revolution frequency

How does NEET ask Atoms?

Which topics in Atoms carry the most questions?

Why does Atoms show "–" until you answer 3 questions?

What happens when you test Atoms?

Chapters either side of Atoms by weight