Question

An element with mass number 81 contains 31.7% more neutrons as compared to protons. Find the symbol of the atom.

• A. ${}_{34}^{81}Se$
• B. ${}_{35}^{81}Br$
• C. ${}_{36}^{81}Kr$
• D. ${}_{37}^{81}Rb$

Answer 1

The correct option is B ${}_{35}^{81}Br$

Mass number of the element =81
i.e. $p+n=81$
Let the number of protons be x.

Number of neutrons = $x+\frac{31.7}{100}\times x=1.317x$

$\therefore x+1.317x=81$ or $2.317x=81$

or $x=\frac{81}{2.317}=35$

Symbol of the element = ${}_{35}^{81}Br$