Topic: UNIT 2: Quantum Mechanical Model of Atom



Topic: UNIT 2: Quantum Mechanical Model of Atom
Q.1
Electronic configuration of species M2+ is 1s2 2s2 2p6 3s2 3p6 3d6 and its atomic weight is 56. The number of neutrons in the nucleus of species M is
A. 26
B. 22
C. 30
D. 24
Answer : Option C
Explaination / Solution:

M2+ : 1s2 2s2 2p6 3s2 3p6 3d6

M : 1s2 2s2 2p6 3s2 3p6 3d8

Atomic number = 26

Mass number =56

No. of neutrons = 56 -26 = 30


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Q.2
The energy of light of wavelength 45 nm is
A. 6.67 × 1015J
B. 6.67 × 1011J
C. 4.42 × 10–18J
D. 4.42 × 10–15J
Answer : Option C
Explaination / Solution:

E = hν = hc/λ

=6.626 × 1034 J s × 3 ×108 m s1  / 45 ×109 m

= 4 .42 ×1018 J


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Q.3
The energies E1 and E2 of two radiations are 25 eV and 50 eV respectively. The relation between their wavelengths ie λ1 and λ2 will be
A. λ12 = 1
B. λ1 = 2λ2
C. λ1 =  √(25 × 50 λ2)
D. 1 = λ2
Answer : Option B
Explaination / Solution:




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Q.4
Splitting of spectral lines in an electric field is called
A. Zeeman effect
B. Shielding effect
C. Compton effect
D. Stark effect
Answer : Option D
Explaination / Solution:

Spliting of spectral lines in magnetic field is called Zeeman effect and spliting of spectral lines in electric field, is called Stark effect.


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Q.5
Based on equation E = – 2.178 × 10–18 J (z2/n2) certain conclusions are written. Which of them is not correct ?
A. Equation can be used to calculate the change in energy when the electron changes orbit
B. For n = 1, the electron has a more negative energy than it does for n = 6 which means that the electron is more loosely bound in the smallest allowed orbit
C. The negative sign in equation simply means that the energy of electron bound to the nucleus is lower than it would be if the electrons were at the infinite distance from the nucleus.
D. Larger the value of n, the larger is the orbit radius.
Answer : Option B
Explaination / Solution:

Correct statement: For n=1, the electron has more negative energy than it does for n=6 which means that the electron is strongly bound in the smallest allowed orbit.

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Q.6
According to the Bohr Theory, which of the following transitions in the hydrogen atom will give rise to the least energetic photon ?
A. n = 6 to n = 1
B. n = 5 to n = 4
C. n = 5 to n = 3
D. n = 6 to n = 5
Answer : Option D
Explaination / Solution:

n = 6 to n=5

E6 = -13.6 / 62 ;

E5 = - 13.6 / 52

E6 - E5 = (-13.6 /62) - (-13.6/52)

= 0.166 eV atom-1

E5 - E4 = (-13.6 /52) - (-13.6/42)

= 0.306 eV atom-1


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Q.7

Assertion : The spectrum of He+ is expected to be similar to that of hydrogen

Reason : He+ is also one electron system.
A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.8
Which of the following pairs of d-orbitals will have electron density along the axes ?
A. dz2, dxz
B. dxz, dyz
C. dz2, dx2-y2
D. dxy, dx2-y2
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.9
Two electrons occupying the same orbital are distinguished by
A. azimuthal quantum number
B. spin quantum number
C. magnetic quantum number
D. orbital quantum number
Answer : Option B
Explaination / Solution:

Spin quantum number

For the first electron ms = +½

For the second electron ms = -½


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Q.10
The electronic configuration of Eu (Atomic no. 63) Gd (Atomic no. 64) and Tb (Atomic no. 65) are
A. [Xe] 4f6 5d1 6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f8 5d1 6s2
B. [Xe] 4f7 , 6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2
C. [Xe] 4f7 , 6s2, [Xe] 4f8 6s2 and [Xe] 4f8 5d1 6s2
D. [Xe] 4f6 5d1 6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2
Answer : Option B
Explaination / Solution:

Eu : [Xe] 4f7, 5d0, 6s2

Gd : [Xe] 4f7, 5d1, 6s2

Tb: [Xe] 4f9, 5d0, 6s2


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