An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.
Mass number = 81 i.e p + n = 81
Let us suppose number of protons = x and neutrons
= x+31.7Xx /100 = 1.317x
Therefore x + 1.317x = 81
Or
2.317x = 81
Or x = 81/2.317 = 35 T
hus number of protons = 35 ,i.e atomic number = 35
Hence the symbol is 8135 Br
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