The hydride gap corresponds to elements of

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

Which of the following acids possesses oxidising,reducing,and complex-forming properties?

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

Which of the following ions are present in the anhydrous mixture of $KF$ and $HF$?

What do you understand by the terms: $(i)$ hydrogen economy,$(ii)$ hydrogenation,$(iii)$ syngas,$(iv)$ water-gas shift reaction,and $(v)$ fuel-cell?