State what information is provided by the formula of calcium hydroxide - $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$.

Write the symbols of the following elements & radicals along with their valencies.

(i): Sodium
(ii): Magnesium
(iii): Chlorine [chloride]
(iv): Nitrate
(v): Sulphite
(vi): Aluminium
(vii): Oxygen [oxide]
(viii): Bromine [bromide]
(ix): Zinc
(x): Sulphur [sulphide]
(xi): Sulphate
(xii): Hydroxide
(xiii): Calcium
(xiv): Carbonate
(xv): Potassium
(xvi): Phosphate
(xvii):Iodine [iodide].

Valency list: i]$1^{+}$ ii] $2^{+}$ iii] $3^{+}$ vi] $1^{-}$ vi] $2^{-}$ vi] $3^{-}$.

Write the chemical formula of the following.

Sodium bromide

Write the chemical formula of the following.

Calcium sulphide.

Write the chemical formula of the following.

Magnesium sulphate

Write the chemical formula of the following:

Aluminium chloride.

Write the chemical formula of the following.

Zinc oxide.