An element with a mass number of $81$ contains $31.7 %$ more neutrons as compared to protons. Identify the element.

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Solution

The correct option is B Br
An element with a mass number of $81$ contains $31.7 %$ more neutrons as compared to protons. The element is bromine.
Let P be the atomic number.
Number of protons $= P$
Number of neutrons $= \frac{100 + 31.7}{100} \times P = 1.317 P$
The mass number is 81. It is the sum of the number of protons and the number of neutrons.
$81 = P + 1.317 P = 2.317 P$
$\Rightarrow P = 35$ .

It is atomic number of bromine.

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\begin{matrix} Column I & Column II i . & Number of protons in the element with mass number 81 & p . & 50 and having 31.7 % more neutrons than protons i i . & Ionic mass of M^{2 +} which is isoelectronic of C O_{2} and has & q . & 26 (Z+2) neutrons . i i i . & Ionic mass of X^{-} with 17 protons and having 11.1 % & r . & 35 more neutrons than electrons i v . & Atomic number of M^{3 +} with mass number 56 and having & s . & 37 30.4 % more neutrons than electrons \end{matrix}

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