Which of the following is distilled first during the fractional distillation of liquid air or mixtures of these gases?

Electrolysis of fused sodium hydride liberates hydrogen at the

In which of the following reactions is dihydrogen not evolved?

Which property among the following is the same for both hydrogen and deuterium molecules?

Which one of the following is the most abundant element in the universe?

Formic acid is heated with conc. $H_2SO_4$ at $100^{\circ}C$ to form $A$ and $B$. When $Fe_2O_3$ is heated strongly with $B$,the products formed are $C$ and $D$. $C$ can also be obtained by reacting $CaCO_3$ with dil. $HCl$. What is $D$?