Test: Atoms and Nuclei - 2 - CUET Humanities MCQ

According to Bohr's hypothesis, electron can revolve only in those orbits in which its angular momentum is an integral multiple of , where h being the Planck's constant. In these orbits, angular momentum of electron can have magnitude as , ... etc. but never as , ..... etc.
This is called quantisation of angular momentum.

Radius of Bohr orbit


 
 
 

From de-Broglie equation, we have
 = 
where λ is wavelength, h is Planck's constant, m is mass, p is momentum and v is velocity.
Given, λ = 10 pm = 10^–11 m, m = 9.1 × 10^–31 kg, h = 6.6 × 10^–34 Js
 v = 
= 
= 7.25 × 10⁷ m/s
Energy of electron
= mv² =  × 
= 15 keV

E = mc² = (0.5 × 10^-3) (3 × 10⁸)² = 4.5 × 10¹³ J = 4.5 × 10¹³/(60 × 60) = 1.25 × 10⁷ kWh

In a controlled nuclear reactor, the moderator used slows down the neutrons produced due to the fission. The element used as the moderator should be able to slow down the neutrons.

A nucleus which is in an excited state may emit one or more photons of discrete energies to attain a stable state. The emission of gamma rays does not alter the number of protons or neutrons in the nucleus.

Decrease in mass number = 222 – 210 = 12
Number of α particles emitted = 12/4 = 3
3α particles will be emitted.


Increase in atomic number = 84 – 80 = 4
Number of β particles emitted = 4
4β particles will be emitted.

The nuclei which have same number of neutrons but different atomic number and mass number are known as isotones.
In choice (1), the nuclei of ₃₄Se⁷⁴ and ₃₁Ga⁷¹ are isotones as:
₃₄Se⁷⁴
A - Z = 74 – 34 = 40
₃₁Ga⁷¹
A - Z = 71 – 31 = 40

In fission process, when a parent nucleus breaks into daughter products, then some mass is lost in the form of energy.
Thus, mass of fission products < mass of parent nucleus.
⇒ (mass of fission products/mass of parent nucleus) < 1