Question

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

Answer 1

We know that mass number of the element,

A = p+n = 81

Let the number of protons, p = x

Then, number of neutrons,

n= x+ 31.7 / 100x = 1.317 x

(As number of neutrons are 31.7% more than the protons.) Hence, from Eq. (i)

x + 1.317 x = 81

x = 81 / 2.317 = 34.958 = 35 (approx)

Therefore, number of protons = 35 and the symbol is ${}_{35}^{81}Br$ (Number of protons = Atomic number)

Answer 2

An element with mass number = 81 i.e p + n = 81

Assume the number of protons = x, and neutrons

= x+31.7Xx /100 = 1.317x

which is x + 1.317x = 81

(Or)

2.317x = 81

(Or) x = 81/2.317 = 35 T

Thus number of protons = 35 ,i.e atomic number = 35

Hence the symbol is 8135 Br.