Which one is a chemical change: Fermentation of fruit juice or diluting fruit juice?

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.

Which of the following is not a physical change?

"$A$ solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed".
$(i)$ Translate the above statement into a chemical equation.

What type of coating is formed on copper articles when they get corroded?

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