What is obtained by the reaction of $HCOOH$ with concentrated $H_2SO_4$?

The element used for welding metals with high melting points is:

High purity $(>99.95\,\%)$ dihydrogen is obtained by:

Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors,which one is most important in this respect?

Which of the following is a poor conductor of electricity?

Identify the correct statements from the following.
$(i)$ The number of hydrogen bonded water molecules in copper sulphate pentahydrate is one.
$(ii)$ Lanthanum and zirconium form non-stoichiometric hydrides.
$(iii)$ In solid form of $H_2O$, each oxygen is surrounded by six oxygen in octahedral positions at a distance of $276 \ pm$.