Two elements $M$ and $N$ belong to group $I$ and $II$ respectively and are in the same period of the periodic table. How do the following properties of $M$ and $N$ vary:
$(a)$ sizes of their atoms?
$(b)$ their metallic characters?
$(c)$ their valencies in forming oxides?
$(d)$ formulae of their chlorides?

(A) The atomic size decreases from left to right across a period. Therefore,the atom of $M$ is larger than the atom of $N$.
$(b)$ Metallic character decreases from left to right across a period. Thus,$M$ is more metallic than $N$.
$(c)$ Elements in group $I$ have a valency of $1$,while elements in group $II$ have a valency of $2$.
$(d)$ Since $M$ has a valency of $1$ and $N$ has a valency of $2$,the formulae of their chlorides are $MCl$ and $NCl_{2}$ respectively.