Question

hydrogen can be placed in group 1 and group 7 of periodic table why ...

Answer 1

Because unlike halogens from group 7 it needs 1 electron to gain nearest noble gas configuration and it has small size and properties like elements of group 1 and it also forms similar ions on losing 1 electron like Na+ , H+ and it also forms stable oxides and halides like alkali metals from group 1 , like H20 , Na2O

Answer 2

hydrogen has properties that match to group 1 like 1 electron in valance shell.
it also has properties that match to group7 likeit needs1 electron to attain noble gas configuration.