$A$ shiny brown coloured element $X$ on heating in air becomes black in colour. Name the element $X$ and the black coloured compound formed.

Write one equation each for decomposition reactions where energy is supplied in the form of heat,light,or electricity.

$Fe_{2}O_{3} + 2Al \rightarrow Al_{2}O_{3} + 2Fe$
The above reaction is an example of a:

Identify the substances that are oxidised and the substances that are reduced in the following reactions.
$(i)$ $4Na(s) + O_2(g) \rightarrow 2Na_2O(s)$
$(ii)$ $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)$

Translate the following statements into chemical equations and then balance them.
$(a)$ Hydrogen gas combines with nitrogen to form ammonia.
$(b)$ Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
$(c)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
$(d)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Why should a magnesium ribbon be cleaned before burning in air?