List any two properties of the elements belonging to the first group of the modern periodic table.

$K$ and $Ca$ have atomic numbers $19$ and $20$ respectively,and they belong to the same period.
$(a)$ Which among them would have a smaller atomic size?
$(b)$ Which one would be more electropositive?
$(c)$ To which group would each of them belong?

The elements $Be$,$Mg$,and $Ca$,each having two electrons in their outermost shells,are in periods $2$,$3$,and $4$ respectively of the modern periodic table. Answer the following questions,giving justification in each case:
$(i)$ Write the group to which these elements belong.
$(ii)$ Name the least reactive element.
$(iii)$ Name the element having the largest atomic radius.

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?

''Elements in Periodic Table show periodicity of properties.'' List any four such properties.

Arrange the following elements in the order of their increasing non-metallic character: $Li, O, C, Be, F$.