Question

Write the electronic of an element whose mass no is 31 and atomic number is 15 what is its valency

Answer 1

Posporus, atomic no. 15,mass no 31,valency,-3 or 5

Answer 2

As the atomic  number  is  15 the valence   of the  element  is  3 because  it's last  shell have 5 electrons  and  to gain  octave  it needs  3 more electrons.