A blue coloured inorganic compound when heated with ${\mathrm{H}}_2\mathrm{S}$, gives black precipitate and an aqueous solution of sulphuric acid. Identify the compound. Give your answer with a balanced chemical equation. 

What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an endothermic or an exothermic reaction? 

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

${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\stackrel{\mathrm{Heat}}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

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

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)$ 

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

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

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

${\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+{\mathrm{BaCl}}_2\left(\mathrm{aq}\right)\to {\mathrm{BaSO}}_4\left(\mathrm{s}\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$

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

$\mathrm{CuO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{\mathrm{Heat}}{\to }\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$ 

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

$\mathrm{Ni}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{Ni}{\left(\mathrm{OH}\right)}_2\downarrow +2{\mathrm{NaNO}}_3\left(\mathrm{aq}\right)$ 

When hydrogen gas burns in presence of oxygen, water is formed and when water is electrolysed then hydrogen and oxygen gases are produced. State the kind of reaction that takes place in the first case.