Which of the following gives the correct increasing order of the atomic radii of $O$,$F$ and $N$?

Arrange the following metals in decreasing order of their atomic size: $Ca, Mg, Ba, Be$.

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.

Arrange the following elements in the order of their decreasing metallic character: $Na, Si, Cl, Mg, Al$.

What would be the nature of oxides formed by the elements on the right-hand side of the periodic table?

Give reasons for the following:
$(a)$ Lithium atom is smaller than Sodium atom.
$(b)$ Chlorine (Atomic Number $17$) is more electronegative than Sulphur (Atomic Number $16$).