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

A halogen?

Answer 1

Halogens are the elements present in group 17 of the periodic table.

The characteristics of halogen is that they have 7 electrons in their outer shell.

The electronic configurations of the given atoms are as follows:

Atoms	Atomic number	Electronic configuration
A	3	2,1
B	9	2,7
C	8	2,6
D	7	2,5

Element A has 9 electron in total, out of which 2 are inner shell electrons and 7 are valence electron. Hence, A is the halogen among these atoms.