Question

An atom has atomic mass 232 and atomic number 90. During the course of disintegration, it emits 2 β-particles and few α-particles. The resultant atom has atomic mass 212 and atomic number 82. How many α-particles are emitted during this process

• A. 5
• B. 6
• C. 7
• D. 8

Answer 1

Answer: (A)

5

Answer 2

The decrease in atomic mass = (232 – 212) = 20

Decrease in mass occurs due to emission of α-particles. Let x be the number of alpha particles emitted.

Mass of 'x' α-particles = 4x

So $4x = 20$ or $x = \frac{20}{4} = 5$

Alternative method: This can also be determined by the application of following equation:

No. of β-particles emitted = 2 × No. of α-particles emitted$- (Z_{\text{Parent}} - Z_{\text{End product}})$

2 = 2 × x – (90 – 82) or x = 5