Question

Which one of the following reactions is NOT a decomposition reaction?

• A. $2\mathrm{AgCl}\left(s\right)\to 2\mathrm{Ag}\left(s\right)+{\mathrm{Cl}}_2\left(g\right)$
• B. ${\mathrm{CaCO}}_3\left(s\right)\to \mathrm{CaO}\left(s\right)+{\mathrm{CO}}_2\left(g\right)$
• C. $H_2\left(g\right)+{\mathrm{Cl}}_2\left(g\right)\to 2\mathrm{HCl}\left(g\right)$
• D. $2H_{2}O\left(l\right)\to 2H_2\left(g\right)+O_2\left(g\right)$

Answer 1

The correct option is C $H_2\left(g\right)+{\mathrm{Cl}}_2\left(g\right)\to 2\mathrm{HCl}\left(g\right)$

In a decomposition reaction, a single reactant breaks down into multiple products.
In $H_2\left(g\right)+{\mathrm{Cl}}_2\left(g\right)\to 2\mathrm{HCl}\left(g\right)$, two reactants combine to form a single product, thus it is a combination reaction.