Explain the "Oxidation" in terms of gain or loss of oxygen with two examples.

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

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

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.

Write a balanced chemical equation with state symbols for the following reactions.
$(i)$ Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
$(ii)$ Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

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