Question

the third period contains only 8elements even though its capacity is 18

Answer 1

HEYA FRIEND,

HERE IS YOUR ANSWER,

The third period contains only 8 elements even though its capacity is 18 because there are only 8 elements which have the same physical and chemical characteristics. And thus having the capacity of 18 elements also, third period has only 8 elements.

HOPE IT HELPS YOU! (^^)

Answer 2

because they have the same physical and chemical characteristics.