Question

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

• A. $^{81}_{34}Se$
• B. $^{81}_{35}Br$
• C. $^{81}_{36}Kr$
• D. $^{81}_{37}Rb$

Answer 1

Answer: (B)

$^{81}_{35}Br$

Answer 2

Mass number of the element $= 81$ i.e., $p + n = 81$ Let the number of protons be $x$. Number of neutrons $=x+\frac{31.7}{100} \times x$ $x=1.317\,x$ $\therefore x + 1.317x = 81$ or $2.317\cdot = 81$ or $x=\frac{81}{2.317}$ $=34.958 \approx 35$ Symbol of the element $=^{81}_{35}Br$