Question

The number of neutrons present in the nucleus of an element X, which is represented as $\begin{array}{c}31\\ 15\end{array}X$ is:

• A. 13
• B. 18
• C. 16
• D. 19

Answer 1

Answer: (C)

16

Atomic number $=15=$ No. of electrons$=$ No. of protons

Mass Number $=$ 31

Number of neutrons + number of protons= Atomic mass number.

$\therefore$ Number of neutrons $=31-$number of protons
$=31-15$
$=16$

Hence, option $C$ is the correct answer.