An element with mass number 81 contains 31.7 more neutrons than protons. What is the element?

Let x be the number of protons. The number of neutrons is x + 0.317x = 1.317x. The mass number is 81. It is equal to the sum of the number of protons and the number of neutrons. 81 = x + 1.317x = 2.317x. Solving for x: x = 81 / 2.317 ≈ 35. Hence, the number of protons is approximately 35. The element with 35 protons is Bromine (Br). Therefore, the symbol is ⁸¹₃₅Br.