Question

Dihydrogen can be prepared by which of the following reactions
(i) Reaction of granulated $Zn$ with dil. $HCl$
(ii) Reaction of $Zn$ with aq. $NaOH$
(iii) By heating calcium hydrogen carbonate

• A. (i) and (iii) only
• B. (i), (ii) and (iii)
• C. (i) and (ii) only
• D. (ii) and (iii) only

Answer 1

Answer: (C)

$\because$ (I) $Zn +2 HCl \text { (dil.) } \rightarrow ZnCl _{2}+ H _{2}$ and
$\because$ (II) $Zn +2 NaOH (a q) \rightarrow Na _{2} ZnO _{2}+ H _{2}$
while calcium hydrogen carbonate, i.e. calcium bicarbonate
$\left[ Ca \left( HCO _{3}\right)_{2}\right\}$ On heating give
$Ca \left( HCO _{3}\right)_{2} \xrightarrow{\Delta} CaCO _{3}+ CO _{2}+ H _{2} O$
As it only exsist in solution and will not give $H_{2}$.
Hence, $(I)$ and $(II)$ only give $H_{2}$, i.e. dihydrogen