In context with the industrial preparation of hydrogen from water gas $(CO + H_2)$,which of the following is the correct statement?

The correct statements among $(a)$ to $(d)$ regarding $H_2$ as a fuel are:
$(a)$ It produces fewer pollutants than petrol.
$(b)$ $A$ cylinder of compressed dihydrogen weighs $\sim 30$ times more than a petrol tank producing the same amount of energy.
$(c)$ Dihydrogen is stored in tanks of metal alloys like $NaNi_5$.
$(d)$ On combustion,the values of energy released per gram of liquid dihydrogen and $LPG$ are $142$ and $50 \ kJ,$ respectively.

Tritium is an isotope of

Which is distilled first?

When sugar is brought into contact with concentrated $H_2SO_4$,it turns black due to .......

Explain the isotopes of hydrogen in short.