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

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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 + \(\frac{x\times 31.7}{100}\) = ( x + 0.317x)

Now, Mass no. of element = No. of protons + No. of neutrons 

81 = x + (x + 0.317x)

= 2.317x 

Or 

x = 81/2.317 = 35 

∴ No. of protons = 35, No. of neutrons = 81 – 35 = 46 

Atomic number of element (Z) = Number of protons = 35

The element with atomic number (Z) 35 is bromine 8135Br.

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