Question

Calculate the number of neutrons present in the nucleus of an element which is represented as ${}_{15}{}^{31}\mathrm{X}$.

Answer 1

Atomic number:

• The total number of protons in an atom's nucleus provides us the atomic number of that atom.
• The letter 'Z' is used to signify it.
• All atoms of the same element have the same number of protons and hence the same atomic number.

Mass number:

• The mass number of an atom is calculated by adding the amount of protons and neutrons.
• The letter 'A' is used to signify it.
• Because protons and neutrons coexist in the nucleus of an atom, they are collectively referred to as nucleons.

Calculation of the number of neutrons present.

• Mass number (A) = No. of protons (Z) $+$ No. of neutrons
• But the mass number is given as $31$ and the number of protons is $15$.
• No. of protons (Z) $+$ No. of neutrons $=31$
• Number of neutrons$=31–$ number of protons
• Number of neutrons $=31–15=16$

Thus, the number of neutrons present in the nucleus of an element ${}_{15}{}^{31}\mathrm{X}$ is $16$.