# (solved)Question 2.42 of NCERT Class XI Chemistry Chapter 2

An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.
(Rev. 30-Sep-2022)

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### Question 2.42NCERT 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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