Ncert Solutions Chemistry Class 11th Chemistry Class 11th Structure of Atoms

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

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1 Answer

Answered by

alok kumar singh | Contributor-Level 10

3 months ago

An element can be identified by its atomic number only. Let us find the atomic number.
Let the number of protons = x
Number of neutrons = x + (x×31.7/100) = 1.371x
Now, Mass no. of element = no. of protons + no. neutrons

⇒ x + 1.317x = 81
⇒ x = 34.958

x ? 35

∴ No. of protons = 35, No. of neutrons = 81 – 35 =46
Atomic number of element (Z) = No. of protons = 35
The element with atomic number (Z) 35 is bromine (₃₅⁷⁹Br)

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