Question

justify the reason for the position of hydrogen firstly in modern periodic table

Answer 1

Hydrogen has a single electron in its valence shell. Thus it can lose an electron to achieve a stable configuration like alkali metals and hence can be placed in group 1 (alkali metals). However, it can also gain an electron to achieve a noble gas arrangement and hence can be placed along with group 17 (halogen family) elements.

So, its configuration resembles the configuration of two different groups - group I and group 17. This is why, the position of hydrogen in the modern periodic table is still a topic of debate. Some people place hydrogen along with alkali metal in group I, while others place hydrogen separately at the top of the table.