Question

Why hydrogen should be placed in group I ?

Answer 1

Hydrogen has single electron and its atomic number is one so its placed first. moreover some of its properties match with alkali metals and so its placed in group 1. ..........

Answer 2

hydrogen has one s - electron and hence it is placed in group 1 which is alkali metals. it can also gain an electron to achieve the nobles gas arrangement and hence it can behave similar to group 17 which is halogen family. but it is a special case so we shall place hydrogen at top of pereiodic table.