State one industrial application of the reduction process.

Which of the following is(are) an endothermic process(es)?
$(i)$ Dilution of sulphuric acid
$(ii)$ Sublimation of dry ice
$(iii)$ Condensation of water vapours
$(iv)$ Evaporation of water

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

You could have noted that when copper powder is heated in a china dish, the surface of copper powder becomes coated with black coloured substance.
$(i)$ Why has this black coloured substance formed?
$(ii)$ What is this black substance?
$(iii)$ Write the chemical equation of the reaction that takes place.

Identify the reducing agent in the following reactions:
$(a)$ $4 NH_{3} + 5 O_{2} \longrightarrow 4 NO + 6 H_{2}O$
$(b)$ $H_{2}O + F_{2} \longrightarrow HF + HOF$
$(c)$ $Fe_{2}O_{3} + 3 CO \longrightarrow 2 Fe + 3 CO_{2}$
$(d)$ $2 H_{2} + O_{2} \longrightarrow 2 H_{2}O$

Why is a combustion reaction considered an oxidation reaction?