Atoms NEET Questions with Solutions

Q: How many questions come from Atoms in NEET 2027?

You can expect 1 to 2 questions in NEET 2027. Common asks: Bohr radius and velocity, energy of n-th orbit, Rydberg formula for spectral lines, ionisation energy of hydrogen, and the angular momentum quantisation L = n h-bar.

Q: What did the Rutherford alpha scattering experiment show?

Most alpha particles passed straight through a thin gold foil with no deflection. A small fraction were deflected by large angles, and roughly 1 in 8000 was deflected backwards. This was impossible if charge were spread out (Thomson model). Rutherford concluded the atom's positive charge and almost all its mass are concentrated in a tiny dense nucleus, with electrons orbiting at large distance.

Q: What is the distance of closest approach?

The minimum distance an alpha particle gets to a nucleus when fired head-on. At this point all KE has been converted to PE: r_0 = (1 / 4 pi epsilon_0) × 2 Z e^2 / E_k, where E_k is the alpha's initial KE.

Q: What are Bohr's postulates?

Three: (1) Electrons move in certain stationary circular orbits and do not radiate, despite being accelerated. (2) The angular momentum of an electron is quantised: L = m v r = n h-bar, n = 1, 2, 3 ... (3) When an electron jumps from a higher orbit to a lower one, it emits a photon of energy h f equal to the difference in orbit energies.

Q: What is the Bohr radius?

a_0 = 0.529 angstrom, the radius of the first orbit (n = 1) of a hydrogen atom (Z = 1). For any hydrogen-like atom: r_n = n^2 a_0 / Z.

Q: What is the energy formula for hydrogen-like atoms?

E_n = -13.6 Z^2 / n^2 eV. n = 1 is the ground state with E = -13.6 eV (for H, Z = 1). The negative sign indicates a bound state. Higher n gives less negative (smaller magnitude), n = ∞ gives E = 0 (electron just freed).

Q: What is the Rydberg formula?

1 / lambda = R Z^2 (1 / n_1^2 - 1 / n_2^2), where n_2 > n_1. R = 1.097 × 10^7 per metre. The formula gives the wavelength of light emitted (or absorbed) when an electron jumps between two levels.

Q: Name the hydrogen spectral series and where they fall.

Lyman (n_1 = 1, UV), Balmer (n_1 = 2, visible: H-alpha 656 nm red, H-beta 486 nm blue-green, H-gamma, H-delta), Paschen (n_1 = 3, IR), Brackett (n_1 = 4, IR), Pfund (n_1 = 5, far IR). Higher n_1 means lower energy → longer wavelength.

Q: What are excitation and ionisation energy?

Excitation energy: energy needed to lift an electron from the ground state to an excited level. For H: ground (n = 1) to first excited (n = 2) requires 10.2 eV. Ionisation energy: energy to remove the electron entirely (n = 1 to n = ∞). For H: 13.6 eV.

Q: How does de Broglie's idea explain Bohr quantisation?

If an electron is a standing wave around the nucleus, the orbit circumference must fit a whole number of wavelengths: 2 pi r = n lambda. Substituting lambda = h / m v gives m v r = n h-bar, exactly Bohr's second postulate. This made the random-looking quantisation rule a wave-resonance condition.

Question 1

Energy of n-th orbit of hydrogen:

Accepted Answer

-13.6/n² eV

Question 2

Angular momentum in Bohr's n-th orbit:

Accepted Answer

n h/2π

Question 3

Bohr radius a_0 ≈

Accepted Answer

0.529 Å

Question 4

Balmer series of H lies in:

Accepted Answer

Visible

Question 5

Ionisation energy of H:

Accepted Answer

13.6 eV

Question 6

Wavelength of H-alpha (n = 3 → 2):

Accepted Answer

656 nm

Question 7

Energy of n = 2 of H:

Accepted Answer

-3.4 eV

Question 8

Rutherford\'s alpha scattering proves:

Accepted Answer

Atom is mostly empty space with a dense nucleus

Question 9

Radius of n-th orbit of H:

Accepted Answer

n² × a_0

Question 10

For He+ (Z = 2), E_1:

Accepted Answer

-54.4 eV

Question 11

Lyman series corresponds to:

Accepted Answer

n_1 = 1

Question 12

Shortest wavelength in Lyman series:

Accepted Answer

91.2 nm

Question 13

Energy needed to excite H from n = 1 to n = 2:

Accepted Answer

10.2 eV

Question 14

Number of de Broglie wavelengths fitting around n-th Bohr orbit:

Accepted Answer

n

Question 15

Number of spectral lines emitted when an electron returns from n = 4 to ground:

Accepted Answer

6

Question 16

Kinetic energy of electron in n-th orbit equals:

Accepted Answer

|E_n|

Question 17

Radius of 2nd orbit of He+ (Z = 2):

Accepted Answer

2 a_0

Question 18

H-α and H-β belong to:

Accepted Answer

Balmer

Question 19

Distance of closest approach is independent of:

Accepted Answer

Mass of alpha

Question 20

Total energy E and kinetic energy K of electron in nth orbit relate as:

Accepted Answer

K = -E

Question 21

Ionisation energy of He+:

Accepted Answer

54.4 eV

Question 22

In Bohr's H atom, longest λ in Lyman series:

Accepted Answer

121.6 nm

Question 23

Bohr postulated that electron orbits are:

Accepted Answer

Quantised in angular momentum

Question 24

Number of lines emitted in transitions back to ground from n = 5:

Accepted Answer

10

Question 25

H atom in n = 3. Energy:

Accepted Answer

-1.51 eV

Question 26

In which series do transitions to n = 3 occur?

Accepted Answer

Paschen

Question 27

Velocity of electron in nth orbit of H:

Accepted Answer

c/(137 n)

Question 28

In α-scattering, alpha that scatters at 180° comes closest to the nucleus. Closest distance:

Accepted Answer

∝ Z

Question 29

Ratio of speeds in 1st and 2nd Bohr orbits of H:

Accepted Answer

2:1

Question 30

Wavelengths in Lyman series are:

Accepted Answer

In UV

AtomsNEET Physics · Class 12 · NCERT Chapter 12

More NEET questions, next chapter

Track Your NEET Score Across All 90 Chapters

AtomsNEET Physics · Class 12 · NCERT Chapter 12

1NEET 2018EasyEnergy of n-th orbit of hydrogen:

2NEET 2019EasyAngular momentum in Bohr's n-th orbit:

3NEET 2020EasyBohr radius a_0 ≈

4NEET 2021EasyBalmer series of H lies in:

5NEET 2022EasyIonisation energy of H:

6NEET 2023MediumWavelength of H-alpha (n = 3 → 2):

7NEET 2024MediumEnergy of n = 2 of H:

8NEET 2017MediumRutherford\'s alpha scattering proves:

9NEET 2018MediumRadius of n-th orbit of H:

10NEET 2019MediumFor He+ (Z = 2), E_1:

11NEET 2020MediumLyman series corresponds to:

12NEET 2021MediumShortest wavelength in Lyman series:

13NEET 2022MediumEnergy needed to excite H from n = 1 to n = 2:

14NEET 2023MediumNumber of de Broglie wavelengths fitting around n-th Bohr orbit:

15NEET 2024MediumNumber of spectral lines emitted when an electron returns from n = 4 to ground:

16NEET 2017MediumKinetic energy of electron in n-th orbit equals:

17NEET 2018MediumRadius of 2nd orbit of He+ (Z = 2):

18NEET 2019MediumH-α and H-β belong to:

19NEET 2020MediumDistance of closest approach is independent of:

20NEET 2021MediumTotal energy E and kinetic energy K of electron in nth orbit relate as:

21NEET 2022MediumIonisation energy of He+:

22NEET 2023MediumIn Bohr's H atom, longest λ in Lyman series:

23NEET 2024MediumBohr postulated that electron orbits are:

24NEET 2017MediumNumber of lines emitted in transitions back to ground from n = 5:

25NEET 2018MediumH atom in n = 3. Energy:

26NEET 2019MediumIn which series do transitions to n = 3 occur?

27NEET 2020MediumVelocity of electron in nth orbit of H:

28NEET 2021MediumIn α-scattering, alpha that scatters at 180° comes closest to the nucleus. Closest distance:

29NEET 2022MediumRatio of speeds in 1st and 2nd Bohr orbits of H:

30NEET 2023MediumWavelengths in Lyman series are:

More NEET questions, next chapter

Track Your NEET Score Across All 90 Chapters