Question

Which one is not a chemical decomposition reaction?

• A. $2{{\mathrm{NaHCO}}_3}_{}\to {\mathrm{Na}}_2{{\mathrm{CO}}_3}_{}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$
• B. $\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$
• C. $2{\mathrm{Pb}}_3{\mathrm{O}}_4\to 6\mathrm{PbO}+4{\mathrm{O}}_2$
• D. ${\mathrm{CuCO}}_3\to \mathrm{CuO}+{\mathrm{CO}}_2$

Answer 1

The correct option is B

$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$

The explanation for the correct option:

• Decomposition reaction: A decomposition reaction is a type of chemical reaction in which a reactant decomposes or breaks down to give one or more than one product.

(B)$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$: This reaction is not a decomposition reaction. It is a displacement reaction.

• A displacement reaction is a type of chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution. Here zinc(Zn) will displace hydrogen(H₂) as zinc is more reactive than hydrogen.

The explanation for the incorrect option:

(A)$2{{\mathrm{NaHCO}}_3}_{}\to {\mathrm{Na}}_2{{\mathrm{CO}}_3}_{}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$: This reaction is a decomposition reaction where sodium bicarbonate decomposes to give sodium carbonate, water, and carbon dioxide.

(C)$2{\mathrm{Pb}}_3{\mathrm{O}}_4\to 6\mathrm{PbO}+4{\mathrm{O}}_2$: This reaction is a decomposition reaction where lead tetraoxide decomposes to lead oxide and oxygen.

(D) ${\mathrm{CuCO}}_3\to \mathrm{CuO}+{\mathrm{CO}}_2$ This reaction is a decomposition reaction where copper carbonate decomposes to copper oxide and carbon dioxide.

Therefore, option (B) is correct.