Question

An atom of mass number $15$ and atomic number $7$ captures an $\alpha$-particle and then emits a proton. The mass number and atomic number of the resulting atom will be respectively

• A. 14 and 2
• B. 15 and 3
• C. 16 and 4
• D. 18 and 8

Answer 1

Answer: (D)

${}_7{X}^{15}+\underset{\text{ Alpha particle }}{{}_{2}H{e}^4}\to \underset{\text{Proton}}{{}_1{H}^1}+{}_Z{Y}^A$
According to the law of conservation of charge, we get
$7+2=1+Z\Rightarrow Z=8$
According to the law of conservation of mass, we get
$15+4=1+A\Rightarrow A=18$
Hence, the resulting atom has mass number 18 and atomic number 8.