### Question 2.42

NCERT Class XI Chemistry

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

Note: Q 2.35 to 2.41 are simple enough. So they have been skipped. Please write an email to us if you face any difficulty with any of them.### Solution in Detail

(video solution below this)

Let protons = $\displaystyle p$

given: $\displaystyle n = p + 31.7\% \text{ of } p $

$\displaystyle \therefore n = 1.317p$

but $\displaystyle n + p = A = 81$ (given)

$\displaystyle \therefore 2.317p = 81$

$\displaystyle \implies p = \frac{81}{2.317} = 35$

$\displaystyle \implies Z = 35 \text{ (bromine)}$

$\displaystyle \therefore $ atom is $\displaystyle ^{81}_{35}\text{Br }\underline{Ans} $

### Video Explanation

Please watch this youtube video for a quick explanation of the solution:

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