Question

the atomic number of chlorine is 17 and mass number is 35 what would be the electronic configuration of a negatively charged chloride ion

Answer 1

Configuration is...
2,8,7
with valency 1

Answer 2

cl=17

Then it's E.C. will be 2,8,7

As it needs ! electron to complete it's octate , So it's E.C. will become

2,8,8    which is of chloride ion.