Question

An element X has mass no.35 & no. of neutrons is 18.Identify the grp no. & period no.of X.

Answer 1

Hey!

Mass Number = Atomic Number + Number of Neutrons
⇒ 35 = Atomic Number of X + 18
⇒ 35 - 18 = Atomic Number of X
⇒ Atomic Number of X = 17

The element with 17 as atomic no. is Chlorine (Cl).
Electronic Configuration of Cl → 2, 8, 7
∴ Valency of Cl = 1

Group Number → 17
Period Number → 3