Question

An atomic nucleus A is composed of 84 protons and 128 neutrons.

The atomic nucleus A emits an alpha particle and is transformed into nucleus B. The atomic nucleus B emits a $\beta$ - particle and is transformed into a nucleus C. What is the composition of atomic nucleus C?

• A. ${}_{83}^{208}C$
• B. ${}_{84}^{208}C$
• C. ${}_{83}^{209}C$
• D. ${}_{85}^{206}C$

Answer 1

The correct option is A

${}_{83}^{208}C$

In nucleus B atomic number is decreased by 2 and the mass number is decreased by 4. Thus, the resulting nucleus has 2 protons and 2 neutrons less than parent (A) nucleus.
${}_{84}^{212}A\to {}_2^{4}He+{}_{82}^{208}B$

While emitting a $\beta$ - particle, the number of nucleons in nucleus C remains the same but the number of neutrons is decreased by one and the number of protons is increased by one.
${}_{82}^{208}B\to {}_{-1}^{0}e+{}_{83}^{208}C$