Atoms Practice Questions - DPP for JEE

 Page 1


PART-I (Single Correct MCQs)
1. In the Bohr’s model of hydrogen-like atom the force between the
nucleus and the electron is modified as  where ß
is a constant. For this atom, the radius of the n
th
 orbit in terms of the
Bohr radius   is:
(a) r
n
 = a
0
n – ß
(b) r
n
 = a
0
n
2
 + ß
(c) r
n
 = a
0
n
2
 – ß
(d) r
n
 = a
0
n + ß
2. In the Bohr model an electron moves in a circular orbit around the
proton. Considering the orbiting electron to be a circular current loop,
the magnetic moment of the hydrogen atom, when the electron is in n
th
Page 2


PART-I (Single Correct MCQs)
1. In the Bohr’s model of hydrogen-like atom the force between the
nucleus and the electron is modified as  where ß
is a constant. For this atom, the radius of the n
th
 orbit in terms of the
Bohr radius   is:
(a) r
n
 = a
0
n – ß
(b) r
n
 = a
0
n
2
 + ß
(c) r
n
 = a
0
n
2
 – ß
(d) r
n
 = a
0
n + ß
2. In the Bohr model an electron moves in a circular orbit around the
proton. Considering the orbiting electron to be a circular current loop,
the magnetic moment of the hydrogen atom, when the electron is in n
th
excited state, is :
(a)
(b)
(c)
(d)
3. In Rutherford scattering experiment, the number of a-particles scattered
at 60° is 5 × 10
6
. The number of a-particles scattered at 120° will be
(a) 15 × 10
6
(b) × 10
6
(c) × 10
6
(d) None of these
4. Electrons in a certain energy level n = n
1
, can emit 3 spectral lines.
When they are in another energy level, n = n
2
. They can emit 6 spectral
lines. The orbital speed of the electrons in the two orbits are in the ratio
of
(a) 4 : 3
(b) 3 : 4
(c) 2 : 1
(d) 1 : 2
5. Energy of an electron in an excited hydrogen atom is –3.4 eV. Its
angular momentum will be
(a) 3.72 × 10
–34
Js
(b) 2.10 × 10
–34
Js
(c) 1.51 × 10
–34
 Js
(d) 4.20 × 10
–34
Js
Page 3


PART-I (Single Correct MCQs)
1. In the Bohr’s model of hydrogen-like atom the force between the
nucleus and the electron is modified as  where ß
is a constant. For this atom, the radius of the n
th
 orbit in terms of the
Bohr radius   is:
(a) r
n
 = a
0
n – ß
(b) r
n
 = a
0
n
2
 + ß
(c) r
n
 = a
0
n
2
 – ß
(d) r
n
 = a
0
n + ß
2. In the Bohr model an electron moves in a circular orbit around the
proton. Considering the orbiting electron to be a circular current loop,
the magnetic moment of the hydrogen atom, when the electron is in n
th
excited state, is :
(a)
(b)
(c)
(d)
3. In Rutherford scattering experiment, the number of a-particles scattered
at 60° is 5 × 10
6
. The number of a-particles scattered at 120° will be
(a) 15 × 10
6
(b) × 10
6
(c) × 10
6
(d) None of these
4. Electrons in a certain energy level n = n
1
, can emit 3 spectral lines.
When they are in another energy level, n = n
2
. They can emit 6 spectral
lines. The orbital speed of the electrons in the two orbits are in the ratio
of
(a) 4 : 3
(b) 3 : 4
(c) 2 : 1
(d) 1 : 2
5. Energy of an electron in an excited hydrogen atom is –3.4 eV. Its
angular momentum will be
(a) 3.72 × 10
–34
Js
(b) 2.10 × 10
–34
Js
(c) 1.51 × 10
–34
 Js
(d) 4.20 × 10
–34
Js
6. The radiation corresponding to 3 ? 2 transition of hydrogen atom falls
on a metal surface to produce photoelectrons. These electrons are made
to enter a magnetic field of 3 × 10
–4 
T. If the radius of the largest
circular path followed by these electrons is 10.0 mm, the work function
of the metal is close to:
(a) 1.8 eV
(b) 1.1 eV
(c) 0.8 eV
(d) 1.6 eV
7. If in hydrogen atom, radius of n
th
 Bohr orbit is r
n
, frequency of
revolution of electron in n
th
 orbit is f
n
, choose the correct option.
(a)
(b)
(c)
(d) Both (a) and (b)
8. A 12.5 eV electron beam is used to bombard gaseous hydrogen at room
temperature. It will emit :
(a) 2 lines in the Lyman series and 1 line in the Balmar series
(b) 3 lines in the Lyman series
(c) 1 line in the Lyman series and 2 lines in the Balmar series
(d) 3 lines in the Balmer series
9. The electric potential between a proton and an electron is given by V =
Page 4


PART-I (Single Correct MCQs)
1. In the Bohr’s model of hydrogen-like atom the force between the
nucleus and the electron is modified as  where ß
is a constant. For this atom, the radius of the n
th
 orbit in terms of the
Bohr radius   is:
(a) r
n
 = a
0
n – ß
(b) r
n
 = a
0
n
2
 + ß
(c) r
n
 = a
0
n
2
 – ß
(d) r
n
 = a
0
n + ß
2. In the Bohr model an electron moves in a circular orbit around the
proton. Considering the orbiting electron to be a circular current loop,
the magnetic moment of the hydrogen atom, when the electron is in n
th
excited state, is :
(a)
(b)
(c)
(d)
3. In Rutherford scattering experiment, the number of a-particles scattered
at 60° is 5 × 10
6
. The number of a-particles scattered at 120° will be
(a) 15 × 10
6
(b) × 10
6
(c) × 10
6
(d) None of these
4. Electrons in a certain energy level n = n
1
, can emit 3 spectral lines.
When they are in another energy level, n = n
2
. They can emit 6 spectral
lines. The orbital speed of the electrons in the two orbits are in the ratio
of
(a) 4 : 3
(b) 3 : 4
(c) 2 : 1
(d) 1 : 2
5. Energy of an electron in an excited hydrogen atom is –3.4 eV. Its
angular momentum will be
(a) 3.72 × 10
–34
Js
(b) 2.10 × 10
–34
Js
(c) 1.51 × 10
–34
 Js
(d) 4.20 × 10
–34
Js
6. The radiation corresponding to 3 ? 2 transition of hydrogen atom falls
on a metal surface to produce photoelectrons. These electrons are made
to enter a magnetic field of 3 × 10
–4 
T. If the radius of the largest
circular path followed by these electrons is 10.0 mm, the work function
of the metal is close to:
(a) 1.8 eV
(b) 1.1 eV
(c) 0.8 eV
(d) 1.6 eV
7. If in hydrogen atom, radius of n
th
 Bohr orbit is r
n
, frequency of
revolution of electron in n
th
 orbit is f
n
, choose the correct option.
(a)
(b)
(c)
(d) Both (a) and (b)
8. A 12.5 eV electron beam is used to bombard gaseous hydrogen at room
temperature. It will emit :
(a) 2 lines in the Lyman series and 1 line in the Balmar series
(b) 3 lines in the Lyman series
(c) 1 line in the Lyman series and 2 lines in the Balmar series
(d) 3 lines in the Balmer series
9. The electric potential between a proton and an electron is given by V =
V
0
 ln  , where r
0
 is a constant. Assuming Bohr’s model to be
applicable, write variation of r
n
 with n, n being the principal quantum
number?
(a) r
n
 ? n
(b) r
n
 ? 1/n
(c) r
n
 ? n
2
(d) r
n
 ? 1/n
2
10. Electron in hydrogen atom first jumps from third excited state to second
excited state and then from second excited to the first excited state. The
ratio of the wavelength  ?
1
 : ?
2
 emitted in the two cases is
(a) 7/5
(b) 27/20
(c) 27/5
(d) 20/7
11. The diagram shows the energy levels for an electron in a certain atom.
Which transition shown represents the emission of a photon with the
most energy?
(a) IV
(b) III
(c) II
(d) I
12. Consider 3
rd
 orbit of He
+
 (Helium), using non-relativistic approach, the
speed of electron in this orbit will be [given K = 9 × 10
9
 constant, Z = 2
and h (Plank’s Constant) = 6.6 × 10
–34
 J s]
(a) 1.46 × 10
6
 m/s
(b) 0.73 × 10
6
 m/s
(c) 3.0 × 10
8
 m/s
Page 5


PART-I (Single Correct MCQs)
1. In the Bohr’s model of hydrogen-like atom the force between the
nucleus and the electron is modified as  where ß
is a constant. For this atom, the radius of the n
th
 orbit in terms of the
Bohr radius   is:
(a) r
n
 = a
0
n – ß
(b) r
n
 = a
0
n
2
 + ß
(c) r
n
 = a
0
n
2
 – ß
(d) r
n
 = a
0
n + ß
2. In the Bohr model an electron moves in a circular orbit around the
proton. Considering the orbiting electron to be a circular current loop,
the magnetic moment of the hydrogen atom, when the electron is in n
th
excited state, is :
(a)
(b)
(c)
(d)
3. In Rutherford scattering experiment, the number of a-particles scattered
at 60° is 5 × 10
6
. The number of a-particles scattered at 120° will be
(a) 15 × 10
6
(b) × 10
6
(c) × 10
6
(d) None of these
4. Electrons in a certain energy level n = n
1
, can emit 3 spectral lines.
When they are in another energy level, n = n
2
. They can emit 6 spectral
lines. The orbital speed of the electrons in the two orbits are in the ratio
of
(a) 4 : 3
(b) 3 : 4
(c) 2 : 1
(d) 1 : 2
5. Energy of an electron in an excited hydrogen atom is –3.4 eV. Its
angular momentum will be
(a) 3.72 × 10
–34
Js
(b) 2.10 × 10
–34
Js
(c) 1.51 × 10
–34
 Js
(d) 4.20 × 10
–34
Js
6. The radiation corresponding to 3 ? 2 transition of hydrogen atom falls
on a metal surface to produce photoelectrons. These electrons are made
to enter a magnetic field of 3 × 10
–4 
T. If the radius of the largest
circular path followed by these electrons is 10.0 mm, the work function
of the metal is close to:
(a) 1.8 eV
(b) 1.1 eV
(c) 0.8 eV
(d) 1.6 eV
7. If in hydrogen atom, radius of n
th
 Bohr orbit is r
n
, frequency of
revolution of electron in n
th
 orbit is f
n
, choose the correct option.
(a)
(b)
(c)
(d) Both (a) and (b)
8. A 12.5 eV electron beam is used to bombard gaseous hydrogen at room
temperature. It will emit :
(a) 2 lines in the Lyman series and 1 line in the Balmar series
(b) 3 lines in the Lyman series
(c) 1 line in the Lyman series and 2 lines in the Balmar series
(d) 3 lines in the Balmer series
9. The electric potential between a proton and an electron is given by V =
V
0
 ln  , where r
0
 is a constant. Assuming Bohr’s model to be
applicable, write variation of r
n
 with n, n being the principal quantum
number?
(a) r
n
 ? n
(b) r
n
 ? 1/n
(c) r
n
 ? n
2
(d) r
n
 ? 1/n
2
10. Electron in hydrogen atom first jumps from third excited state to second
excited state and then from second excited to the first excited state. The
ratio of the wavelength  ?
1
 : ?
2
 emitted in the two cases is
(a) 7/5
(b) 27/20
(c) 27/5
(d) 20/7
11. The diagram shows the energy levels for an electron in a certain atom.
Which transition shown represents the emission of a photon with the
most energy?
(a) IV
(b) III
(c) II
(d) I
12. Consider 3
rd
 orbit of He
+
 (Helium), using non-relativistic approach, the
speed of electron in this orbit will be [given K = 9 × 10
9
 constant, Z = 2
and h (Plank’s Constant) = 6.6 × 10
–34
 J s]
(a) 1.46 × 10
6
 m/s
(b) 0.73 × 10
6
 m/s
(c) 3.0 × 10
8
 m/s
(d) 2.92 × 10
6
 m/s
13. An electron of a stationary hydrogen atom passes from the fifth energy
level to the ground level. The velocity that the atom acquired as a result
of photon emission will be : (m is the mass of the electron, R, Rydberg
constant and h Planck’s constant)
(a)
(b)
(c)
(d)
14. If ?
1
 is the frequency of the series limit of Lyman series, ?
2
 is the
frequency of the first line of Lyman series and ?
3
 is the frequency of the
series limit of the Balmer series then
(a) ?
1
 - ?
2 
=
 
?
3
(b) ?
1
 = ?
2 
-
 
?
3
(c)
(d)
15. Hydrogen (
1
H
1
), Deuterium (
1
H
2
), singly ionised Helium (
2
He
4
)
+
 and
doubly ionised lithium (
3
Li
6
)
++
 all have one electron around the nucleus.
Consider an electron transition from n = 2 to n = 1. If the wavelengths
of emitted radiation are ?
1
, ?
2
, ?
3
 and ?
4
 respectively then approximately
which one of the following is correct?
(a) 4?
1
 = 2?
2
 = 2?
3
 = ?
4
(b) ?
1
 = 2?
2
 = 2?
3
 = ?
4
(c) ?
1
 = ?
2
 = 4?
3
 = 9?
4