Non-stoichiometric hydrides are formed by

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 $D$?

Match List-$I$ (Fuels) with List-$II$ (Composition) and select the correct answer using the codes given below the lists.

List-$I$ (Fuels)	List-$II$ (Composition)
$A$. Water gas	$i$. $A$ mixture of $CO$ and $N_2$
$B$. Producer gas	$ii$. Methane
$C$. Coal gas	$iii$. $A$ mixture of $CO$ and $H_2$
$D$. Natural gas	$iv$. $A$ mixture of $CO$,$H_2$,$CH_4$ and $CO_2$

Choose the correct sequence for $A-B-C-D$ respectively:

Give the chemical reaction for the preparation of producer gas.

What is Carbogen?

Pure dihydrogen $(99.95\%)$ is obtained by the electrolysis of