An element with mass number 81 contains 131.7% more neutrons as compared to protons. The atomic number of element is

Mass number (N + P) = 81Let number of Protons = PThen, neutrons = (81 - N)Also, N=P×131.7100=1.317P∴ P+N=81⇒ P+1.317P=81 ⇒ 2.317P=81 P=34.96≈35 (whole number)   Thus, protons =35 (It is Br ) and neutrons =81−35=46  Hence, atomic symbol is  3581Br.