What happens when a piece of $Zn$ metal is added to $CuSO_4$ solution?

Explain the type of reactions represented by the following equations:
$(i)$ $CaO + CO_2 \longrightarrow CaCO_3$
$(ii)$ $2Na + 2H_2O \longrightarrow 2NaOH + H_2$

Can oxidation or reduction take place alone? Why or why not? What are such reactions called?

Write a balanced chemical equation for the process of photosynthesis and the conditions of the reaction,including the physical states of all the substances.

Write the essential condition for the following reaction to take place: $2 AgCl \rightarrow 2 Ag + Cl_{2}$ and write one use of this reaction.

Translate the following statements into chemical equations and then balance them.
$(a)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
$(b)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.