Which is the oxidising agent in the following reaction?
$CuO(s) + H_2(g) \longrightarrow Cu(s) + H_2O(l)$

Complete and balance the following chemical equations:
$(i)$ $CaCO_{3} + HCl \longrightarrow$
$(ii)$ $Al + HCl \longrightarrow$
$(iii)$ $MnO_{2} + HCl \longrightarrow$

$A$ solution of potassium chloride when mixed with silver nitrate solution,an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

Which of the following are combination reactions?
$(i) 2 KClO_3 \xrightarrow{\text{Heat}} 2 KCl + 3 O_2$
$(ii) MgO + H_2O \longrightarrow Mg(OH)_2$
$(iii) 4 Al + 3 O_2 \longrightarrow 2 Al_2O_3$
$(iv) Zn + FeSO_4 \longrightarrow ZnSO_4 + Fe$

Name the type of reaction for the following:
$(i)$ Silver items turning black when left exposed to air.
$(ii)$ Change in colour of copper sulphate from blue to green on dipping an iron nail in it.

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.