The calorific value of producer gas is low because of:

Which of the following is true for heavy water?

Which among the following is/are primary component$(s)$ of the synthesis gas?

Observe the following reactions:
$I$. $CO_{(g)} + H_{2(g)} \xrightarrow{X} HCHO_{(g)}$
$II$. $CO_{(g)} + 3 H_{2(g)} \xrightarrow{Y} CH_{4(g)} + H_2O_{(g)}$
The catalysts $X$ and $Y$ in the above reactions are respectively:

How many of the following statements is/are correct?
$(a)$ Mercury is the only metal that exists as liquid at room temperature.
$(b)$ Among non-metals,carbon has the highest melting point.
$(c)$ Hydrogen is the most abundant element in the universe.
$(d)$ Oxygen is the most abundant element in the earth's crust.

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.