Question

an element X has mass number 35 and the number of neutron is 18 identify the group number and period of x

Answer 1

Atomic number of X = Mass number of X -No. of neutrons
=35- 18 = 17
Electronic configuration = 2,8,7

Group no. 17 and period no. =3
Chlorine

Answer 2

chlorine has mass no.35