(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.

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Parveen,

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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