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) $Zn+2HCl\text{ (dil.) }\to ZnC{l}_2+H_2$ and
$\because$ (II) $Zn+2NaOH(aq)\to N{a}_{2}Zn{O}_2+H_2$
while calcium hydrogen carbonate, i.e. calcium bicarbonate
$\left[Ca{\left(HC{O}_3\right)}_2\right\}$ On heating give
$Ca{\left(HC{O}_3\right)}_2\stackrel{\Delta }{\to }CaC{O}_3+C{O}_2+H_{2}O$
As it only exsist in solution and will not give $H_2$.
Hence, $(I)$ and $(II)$ only give $H_2$, i.e. dihydrogen