NEET Previous Year Questions (2014-2023): Atoms

# NEET Previous Year Questions (2014-2023): Atoms | Physics Class 12 PDF Download

## 2023

Q.1. The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of V volts is proportional to         (2023)
(a) √V
(b) 1/V
(c) 1/√V
(d) V2
Ans:
b

Q.2. In hydrogen spectrum, the shortest wavelength in the Balmer series is λ. The shortest wavelength in the Bracket series is         (2023)
(a) 2λ
(b) 4λ
(c) 9λ
(d) 16λ
Ans:
b

λ = 4/R ...(1)
For Bracket, (n2 = 4, n1 = ∞)

λ' = 16/R ...(2)

Q.3. The radius of inner most orbit of hydrogen atom is 5.3 × 10 –11 m. What is the radius of third allowed orbit of hydrogen atom?         (2023)
(a) 0.53 Å
(b) 1.06 Å
(c) 1.59 Å
(d) 4.77 Å
Ans:
d

r2 = 9r1 = 5.3 x 10-11 x 9
= 47.7 × 10–11
= 4.77 Å

## 2022

Q.4. Let T1 and T2 be the energy of an electron in the first and second excited states of hydrogen atoms, respectively. According to Bohr’s model of an atom, the ratio T1 : T2 is         (2022)
(a) 4 : 1
(b) 4 : 9
(c) 9 : 4
(d) 1 : 4
Ans: c

En = E/ n2
For first excited state: n = 2
For second excited state  n = 3

## 2020

Q.5. For which one of the following, Bohr model is not valid?     (2020)
(a) Deuteron atom
(b) Singly ionised neon atom (Ne+)
(c) Hydrogen atom
(d) Singly ionised helium atom (He+)
Ans:
b

Bohr Model is valid only for those atoms which have one electron in orbit.

Bohr Model

## 2019

Q.6. The total energy of an electron in an atom in an orbit is –3.4 eV. Its kinetic and potential energies are, respectively:    (2019)
(a) –3.4 eV, –3.4 eV
(b) –3.4 eV, –6.8 eV
(c) 3.4 eV, –6.8 eV
(d) 3.4 eV, 3.4 eV
Ans
: c

In Bohr's model of H atom

∴ K.E. = 3.4 eV
U = –6.8 eV

Q.7. α-particle consists of :    (2019)
(a) 2 protons and 2 neutrons only
(b) 2 electrons, 2 protons and 2 neutrons
(c) 2 electrons and 4 protons only
(d) 2 protons only
Ans:
a

α-particle is nucleus of Helium which has two protons and two neutrons.

## 2018

Q.8. The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom,is :-    (2018)
(a) 1 : 1
(b) 1 : –1
(c) 2 : –1
(d) 1 : –2
Ans:
b

## 2017

Q.9. Suppose the charge of a proton and an electron differ slightly. One of them is – e, the other is(e + De). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then De is of the order of [Given mass of hydrogen mh = 1.67 × 10–27 kg]     (2017)
(a) 10–23 C
(b) 10–37 C
(c) 10–47 C
(d) 10–20 C
Ans:
b

We know, a hydrogen atom has one electron and one proton
so, net charge on each hydrogen atom = (e + ∆e - e) = ∆e
so, electrostatic force ,
gravitational force,
where Mh denotes mass of hydrogen
a/c to question,
gravitational force = electrostatic force

we know, K = 9 × 109 Nm²/C², G = 6.67 × 10-11 Nm²/Kg² , Mh = 1.67 × 10-27 Kg
so, 9 × 109 × ∆e² = 6.67 × 10-11 × (1.67 × 10-27)²
or, ∆e² = 6.67 × 10-11 × 1.67 × 1.67 × 10-54/9 × 109
or, ∆e = 1.43767 × 10-37 C

Q.10. The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is :-     (2017)
(a) 1
(b) 4
(c) 0.5
(d) 2
Ans:
b

For last line of Balmer : n1 = 2 & n2 = ∞

For last line Lyman series : n1 = 1 & n2 = ∞

## 2016

Q.11. When an α-particle of mass 'm' moving with velocity 'v' bombards on a heavy nucleus of charge 'Ze' its distance of closet approach from the nucleus depends on m as :    (2016)
(a) m
(b) 1/m
(c) 1/√m
(d) 1/m2
Ans:
b

When an alpha particle moving with velocity v bombards on a heavy nucleus of charge Ze, then there will be no loss of energy.
Initial Kinetic energy of the alpha particle = Potential energy of alpha particle at closest approach.
That is,

This is the required distance of closest approach to alpha particle from the nucleus.
When an alpha particle moving with velocity v bombards on a heavy nucleus of charge Ze, then there will be no loss of energy.
Initial Kinetic energy of the alpha particle = Potential energy of alpha particle at closest approach.
That is,

This is the required distance of closest approach to alpha particle from the nucleus.

Q.12. Given the value of Rydberg constant is 107 m-1, the wave number of the last line of the Balmer series in hydrogen spectrum will be :     (2016)
(a) 2.5 x 107m-1
(b) 0.025 x 104m-1
(c) 0.5 x 107m-1
(d) 0.25 x 107m-1
Ans:
d

Rydberg constant, r = 107 m-1
For last line in Balmer series,
n2 = ∞; n1 = 2
We know,

## 2015

Q.13. Consider 3rd orbit of He+ (Helium), using non-relativistic approach, the speed of electron in this orbit will be [given K = 9 x 109 constant, Z = 2 and h(Planck's Constant) = 6.6 x 10-34 J s]    (2015)
(a) 3.0 x 108 m/s
(b) 2.92 x 106 m/s
(c) 1.46 x 106 m/s
(d) 0.73 x 106 m/s
Ans:
c

Q.14. If radius of thenucleus is taken to be RAl, then the radius ofnucleus is nearly :    (2015)

(a)

(b)

(c)

(d)

Ans:
c

Radius of the nucleus goes as R ∝ A1/3, where A is the atomic mass. If RTe is the radius of the nucleus of telurium atom and RAl is the radius of the nucleus of aluminium atom we have

## 2014

Q.15. Hydrogen atom in ground state is excited by a monochromatic radiation of λ = 975 Å. Number of spectral lines in the resulting spectrum emitted will be:     (2014)
(a) 6
(b) 10
(c) 3
(d) 2
Ans:
a

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## Physics Class 12

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## FAQs on NEET Previous Year Questions (2014-2023): Atoms - Physics Class 12

 1. What is an atom?
Ans. An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus containing protons and neutrons, with electrons orbiting around the nucleus.
 2. How many protons, neutrons, and electrons are present in a typical atom?
Ans. A typical atom has an equal number of protons and electrons, which determine its atomic number. Neutrons are also present in the nucleus but their number can vary, leading to different isotopes of the same element.
 3. What is the significance of the atomic number of an element?
Ans. The atomic number of an element represents the number of protons in the nucleus of its atom. It determines the chemical properties and identity of the element, as elements with different atomic numbers have different properties.
 4. How do electrons occupy different energy levels in an atom?
Ans. Electrons occupy specific energy levels or shells around the nucleus of an atom. They fill the innermost shell first before moving to higher energy levels, following the rules of the Aufbau principle, Pauli exclusion principle, and Hund's rule.
 5. What is the difference between an atom and an ion?
Ans. An atom is a neutral particle with an equal number of protons and electrons. An ion, on the other hand, is a charged particle that has gained or lost electrons, leading to an imbalance of positive or negative charge.

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