What is the periodic trend in the variation of valency while going down a group? Explain your answer with reserence to the group 1, group 2 and group 18.

Explanation

The velency of an element is determined by the number of valuence elenctrons persent in the outermost shell of an atom of an element.
All the elements in a grop have the same numbr of valence elements. Therefore, elements in the same group should have the same valency.
For example, the elements of group , the valence electron, the valency of elements of group 1 is one. Similarly for group 2, (Be, Mg, Ca ) contain two valence electrons, the valency of elements of group 2 in two.
The elements of group 18 (Ne ,Ar ) contain 8 electrons (exception, Helium contain 2 electrons). Since the octect is complected their valency is zero.