Question

Four atoms are labelled from A to D:

Atoms	Mass No.	Atomic no.
A	19	9
B	7	3
C	16	8
D	14	7

Element having 3 valency.

Answer 1

The combining capacity is called valency. It can be calculated by counting the valence electrons ( electrons present in the outer shell ).

• If the atom has 4 or less than 4 electrons- the valency is equal to the number of valence electron
• If the atom has more than 4 electrons- the valency is [8-(number of valence electrons)]

The electronic configuration of

1. A is 2,7; valency:1
2. B is 2,1; valency: 1
3. C is 2,6; valency: 2
4. D is 2,5; valency:3

Hence, the answer element D