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

Mass number of element $=81i.e.,p+n=81$

Let the number of protons be x.

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

$\therefore x+1.317x=81or2.317x=81$ Or $x=\frac{81}{2.317}=35$

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