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Q.
An element with mass number $81$ contains $31.7\%$ more neutrons as compared to protons. Find the symbol of the atom
Structure of Atom
Solution:
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 $=^{81}_{35}Br$