By passing electric current through water, ${\mathrm{H}}_2$ and ${\mathrm{O}}_2$ are obtained as: 

$2{\mathrm{H}}_2\mathrm{O}\stackrel{\mathrm{electric} \mathrm{current}}{\to }2{\mathrm{H}}_2+{\mathrm{O}}_2$

But ${\mathrm{H}}_2$ and ${\mathrm{O}}_2$ can also be combined to form water

$2{\mathrm{H}}_2+{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}$

The first reaction is a decomposition reaction and the second reaction is a combination reaction. Is this statement true? Justify.

Classify the following reaction as combination, decomposition or displacement reaction:

${\mathrm{CH}}_4 \stackrel{\mathrm{catalyst}}{\to } \mathrm{C} +2{\mathrm{H}}_2$

Classify the following reaction as combination, decomposition or displacement reaction:

${\mathrm{SO}}_2 +{\mathrm{H}}_2\mathrm{O} \to {\mathrm{H}}_2{\mathrm{SO}}_3$

Classify the following reaction as combination, decomposition or displacement reaction:

$2\mathrm{Na} + 2{\mathrm{H}}_2\mathrm{O} \to 2\mathrm{NaOH} +{\mathrm{H}}_2$

Classify the following reaction as combination, decomposition or displacement reaction:

$\mathrm{Zn}\left(\mathrm{s}\right) + 2{\mathrm{AgNO}}_3\left(\mathrm{aq}\right) \to \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right) +2\mathrm{Ag}\left(\mathrm{s}\right)$

Translate the following into the language of chemistry: 

Sulphur dioxide reacts with oxygen at $450°\mathrm{C}$in the presence of a catalyst $\left({\mathrm{V}}_2{\mathrm{O}}_5\right)$to form sulphur trioxide. The reaction is reversible and $182\mathrm{kJ}$of energy is liberated.

Correct the equation and then balance it:

$$\begin{gathered} \mathrm{Ca} +{\mathrm{H}}_2\mathrm{O} \to \mathrm{CaOH} +{\mathrm{H}}_2 \\ {\mathrm{N}}_{2 } +\mathrm{H} \to {\mathrm{NH}}_3 \end{gathered}$$