Arrange the following elements in the order of their increasing nonmetallic character:
$Li, O, C, Be, F$

$(i)$ State Modern Periodic Law.
$(ii)$ How many :
$(a)$ groups and
$(b)$ periods are present in the modern periodic table?
$(iii)$ State how the problem of placing:
$(a)$ hydrogen,
$(b)$ isotopes of an element has been solved in this periodic table.

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

Which of the following statements is not correct regarding the trends observed when moving from left to right across the periods of the Periodic Table?

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

The scientist who showed that the atomic number of an element is a more fundamental property than its atomic mass is: