# An Element with Mass Number 81 Contains 31.7% More Neutrons as Compared to Protons. Assign the Atomic Symbol. - Chemistry

Numerical

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

#### Solution

Let the number of protons in the element be x.

∴ Number of neutrons in the element

= x + 31.7% of x

= x + 0.317 x

= 1.317 x

According to the question,

Mass number of the element = 81

∴ (Number of protons + number of neutrons) = 81

=> x + 1.317x = 81

2.317x = 81

x = 81/2.317

= 34.95

therefore x = 35

Hence, the number of protons in the element i.e., x is 35.

Since the atomic number of an atom is defined as the number of protons present in its nucleus, the atomic number of the given element is 35.

∴ The atomic symbol of the element is ""_35^81"Br"

Concept: Atomic Mass
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Chapter 2: Structure of Atom - EXERCISES [Page 71]

#### APPEARS IN

NCERT Chemistry Part 1 and 2 Class 11
Chapter 2 Structure of Atom
EXERCISES | Q 2.42 | Page 71
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