The hydrides of which group elements of the periodic table form electron-precise hydrides?

The maximum sum of the number of neutrons and protons in an isotope of hydrogen is

$H_2C_2O_4 \xrightarrow{\Delta} \text{gas } (A) + \text{gas } (B) + \text{liquid } (C)$.
Gas $(A)$ burns with a blue flame and is oxidised to gas $(B)$.
Gas $(A) + Cl_2 \to (D)$.
$A, B$ and $D$ are:

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:

Discuss the consequence of high enthalpy of $H-H$ bond in terms of chemical reactivity of dihydrogen.

Which is an example of a molecular hydride?