Question

why is hydrogen placed in the 1st group though it has the properties of both halogens and alkali metals?

Answer 1

Position of hydrogen in the modern periodic table is controversial. The properties of hydrogen are different from the other members of its group i.e. the alkali metals & do not justify its position in the group (such as its oxide is neutral where as the oxides of alkali metals are basic, alkali metals are most electropositive elements in the table unlike hydrogen), hydrogen forms compounds containing H^- ion like halogens where as alkali metals never form negative ions etc.

So properties of hydrogen are somewhat similar to halogens, so its position is controversial.