Hi Anilbabu,

Given in the question are

Element with mass number is 81

Neutron content 31.7% more compared to protons

Now, Mass Number = 81

i.e., Number of protons + Number of neutrons = 81  .....(1)

Let the number of proton be x

Neutron will be = x + (31.7/100) x = 1.317x

Putting the value in (1)

=> x + 1.317x = 81

=> x = 81/2.317

=> 35

So, protons is 35.

Symbol of the element will be 81Br35