The electronic configuration of an element X is 2,8,8,2. What are its period number, group number and valency, respectively?

It belongs to the 4^th period because its electrons are filled in 4 shells around the nucleus. It is positioned in group 2 because it has 2 valence electrons in the outermost shell. It can lose 2 valence electrons easily to achieve a stable electronic configuration.

So, its valency can be considered as 2.
Hence, Element X belongs to the 4^th period, group 2, and has valency 2.
Electronic configuration of the element X is 2,8,8,2.