An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.

Explanation

No. of protons+no. of neutrons=mass number=81
Let, the number of protons present in an atom=x
Number of neutrons present`=x+(31.7)/(100)xx x=1.317x`
As given in the question, `x+1.317x=81`
or, `2.317x=81` or, `x=34.96=35`
Thus, number of protons=35 i.e., atomic number=35
the element with atomic number 35 is Br.
`therefore`The symbol is `""_(35)^(81)Br`.