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. ${}_{35}^{18}Br$
• C. ${}_{36}^{18}Kr$
• D. ${}_{37}^{18}Rb$

Answer 1

Answer: (B)

${}_{35}^{18}Br$

Answer 2

: 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 $=_{35}^{81}Br$