Atoms and Nuclei questions and answers

Atoms and Nuclei
1. The total energy of an electron in an atom in an orbit is −3.4eV Its kinetic and
potential energies are, respectively
(a) 3.4eV , 3.4eV
(b) −3.4eV , −3.4eV
(c) −3.4eV , −6.8eV
(d) 3.4eV , −6.8eV (NEET2019)
2. 2.  − particle consists of
(a) 2 protons only
(b) 2 protons and 2 neutrons only
(c) 2 electrons, 2 protons and 2 neutrons
(d) 2 electrons and 4 protons only(NEET 2019)
3. The radius of the first permitted Bohr orbit for the electron, in a hydrogen atom equals
0.51 A and its ground state energy equals −13.6e V If the electron in the hydrogen

atom is replaced by muon (  − ) [charge same as electron and mass 207me ], the first

Bohr radius and ground state energy will be
(a) 0.53 10−13 m, −3.6eV
(b) 25.6 10−13 m, −2.8eV
(c) 2.56 10−13 m, −2.8keV
(d) 2.56 10−13 m, −13.6eV (Odisha NEET 2019)
4. The rate of radioactive disintegration at an instant for a radioactive sample of half life
2.2 109 s is 1010 s −1 . The number of radioactive atoms in the sample at that instant is,
(a) 3.17 1020
(b) 3.17 1017
(c) 3.17 1018
(d) 3.17 1019 (Odisha NEET 2019)
5. For a radioactive material, half‐life is 10 minutes. If initially there are 600 number of
nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is
(a) 20
(b) 10
(c) 30
(d) 15 (NEET 2018)
6. The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the
hydrogen atom, is
(a) 1:1
(b) 1: −1
(c) 2: −1
(d) 1: −2 (NEET 2018)

,7. Radioactive material‘ A ’ has decay constant ‘8  ’ and material‘ B ’ has decay
constant‘ ’. Initially they have same number of nuclei. After what time, the ratio of
1
number of nuclei of material‘ B ’ to that‘ A ’ will be ?
e
1
(a)
7
1
(b)
8
1
(c)
9
1
(d) (NEET 2017)

8. The ratio of wavelengths of the last line of Balmer series and the last line of Lyman
series is
(a) 1
(b) 4
(c) 0.5
(d) 2 (NEET 2017)
9. If an electron in a hydrogen atom jumps from the 3rd orbit to the 2nd orbit, it emits a
photon of wavelength  . When it jumps from the 4th orbit to the 3rd orbit, the
corresponding wavelength of the photon will be
16
(a) 
25
9
(b) 
16
20
(c) 
7
20
(d)  (NEET‐II 2016)
13
10. The half‐life of a radioactive substance is 30 minutes. The time (in minutes) taken
between 40% decay and 85% decay of the same radioactive substance is
(a) 15
(b) 30
(c) 45
(d) 60 (NEET‐II 2016)
11. 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
(a) 0.25 107 m −1
(b) 2.5 107 m −1

, (c) 0.025 104 m −1
(d) 0.5 107 m −1 (NEET‐I 2016)
12. When an  ‐particle of mass m moving with velocity v bombards on a heavy
nucleus of charge Ze , its distance of closest approach from the nucleus depends on m
as
1
(a)
m2
(b) m
1
(c)
m
1
(d) (NEET‐I 2016)
m
13. A nucleus of uranium decays at rest into nuclei of thorium and helium. Then
(a) The helium nucleus has more momentum than the thorium nucleus.
(b) The helium nucleus has less kinetic energy than the thorium nucleus.
(c) The helium nucleus has more kinetic energy than the thorium nucleus.
(d) The helium nucleus has less momentum than the thorium nucleus. (2015)
14. Consider 3rd orbit of He + (Helium), using non‐relativistic approach, the speed of
electron in this orbit will be [given K = 9 109 constant, Z = 2 and h (Planck’s
Constant) = 6.6 10−34 Js ]
(a) 0.73 106 m / s
(b) 3.0  108 m / s
(c) 2.92 106 m / s
(d) 1.46 106 m / s (2015 Cancelled)
15. Hydrogen atom in ground state is excited by a monochromatic radiation of  = 975Å .
Number of spectral lines in the resulting spectrum emitted will be
(a) 3
(b) 2
(c) 6
(d) 10 (2014)

16. The binding energy per nucleon of 7
3 Li and 4
2 He nuclei are 5.60 MeV and 7.06 MeV


respectively In the nuclear reaction 37 Li + 11H → 42 He + 42 He + Q the value of energy Q

released is
(a) 19.6MeV
(b) −2.4MeV
(c) 8.4MeV
(d) 17.3MeV (2014)

, 17. A radioisotope X with a halflife 1.4  109 years decays to Y which is stable. A sample
of the rock from a cave was found to contain X and Y in the ratio 1 : 7. The age of the
rock is
(a) 1.96  109 years
(b) 3.92 109 years
(c) 4.20 109 years
(d) 8.40 109 years (2014)
18. Ratio of longest wave lengths corresponding to Lyman and Balmer series in hydrogen
spectrum is
7
(a)
29
9
(b)
31
5
(c)
27
5
(d) (NEBT 2013)
23
19. A certain mass of Hydrogen is changed to Helium by the process of fusion. The mass
defect in fusion reaction is 0.02866 u . The energy liberated per u is ( given 1
u = 931MeV )
(a) 6.675 MeV
(b) 13.35 MeV
(c) 2.67 MeV
(d) 26.7 MeV (NEET 2013)
20. The half life of a radioactive isotope ‘X’ is 20 years. It decays to another element ‘ Y
which is stable. The two elements ‘X’ and ‘ Y were found to be in the ratio 1 : 7 in
a sample of a given rock. The age of the rock is estimated to be
(a) 80 years
(b) 100 years
(c) 40 years
(d) 60 years(NEET 2013)
21. How does the Binding Energy per nucleon vary with the increase in the number of
nucleons?.
(a) Decrease continuously with mass number.
(b) First decreases and then increases with increase in mass number.
(c) First increases and then decreases with increase in mass number.
(d) Increases continuously with mass number. (Karnataka NEET 2013)
22. An electron in hydrogen atom makes a transition n1 → n2 where n1 and n2 are
principal quantum numbers of the two states. Assuming Bohr’s model to be valid, the