# UNIT 2: Quantum Mechanical Model of Atom - Online Test

Q1. 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
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

Q2. The energy of light of wavelength 45 nm is
Explaination / Solution:

E = hν = hc/λ

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

= 4 .42 ×1018 J

Q3. 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
Explaination / Solution:

Q4. Splitting of spectral lines in an electric field is called
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.

Q5. Based on equation E = – 2.178 × 10–18 J (z2/n2) certain conclusions are written. Which of them is not correct ?
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.

Q6. According to the Bohr Theory, which of the following transitions in the hydrogen atom will give rise to the least energetic photon ?
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

Q7.

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

Reason : He+ is also one electron system.
Explaination / Solution:
No Explaination.

Q8. Which of the following pairs of d-orbitals will have electron density along the axes ?
Explaination / Solution:
No Explaination.

Q9. Two electrons occupying the same orbital are distinguished by
Explaination / Solution:

Spin quantum number

For the first electron ms = +½

For the second electron ms = -½

Q10. The electronic configuration of Eu (Atomic no. 63) Gd (Atomic no. 64) and Tb (Atomic no. 65) are
Explaination / Solution:

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

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

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