Define the term solution. How many types of solutions are formed? Write briefly about each type with an example.

(N/A) solution is a homogeneous mixture of two or more chemically non-reacting substances.
There are $9$ types of solutions based on the physical state of the solute and solvent:
$1$. Gaseous solutions:
$(a)$ Gas in gas: Air (mixture of $O_2$ and $N_2$).
$(b)$ Liquid in gas: Water vapour in air.
$(c)$ Solid in gas: Camphor vapours in $N_2$ gas.
$2$. Liquid solutions:
$(a)$ Gas in liquid: $CO_2$ dissolved in water (aerated water).
$(b)$ Liquid in liquid: Ethanol dissolved in water.
$(c)$ Solid in liquid: Sugar dissolved in water.
$3$. Solid solutions:
$(a)$ Gas in solid: Hydrogen gas adsorbed on Palladium $(Pd)$.
$(b)$ Liquid in solid: Amalgam of Mercury with Sodium $(Na-Hg)$.
$(c)$ Solid in solid: Gold ornaments (Copper or Silver alloyed with Gold).