Mass of the solute = 25 g
Mass of the solvent = 100 g
\(\begin{aligned} \text { Mass Percentage } \end{aligned}=\frac{\text { Mass of the solute }}{\text { Mass of the solution }} \times 100\)
\(\begin{aligned} \text { Mass Percentage } \end{aligned}=\frac{\text { Mass of the solute }}{\begin{array}{l} \text { Mass of the solute }+ \text { Mass of the solvent } \end{array}} \times 100\)
\(=\frac {25}{25+100}\times\)100
= \(\frac{25}{125}\times\)100
= 20%

(i) Ionic substances crystallize out from their saturated aqueous solution with a definite number of molecules of water.
(ii) The number of water molecules found in the crystalline substance is called water of crystallization.
(iii) Such salts are called hydrated salts.
(iv) E.g. Blue vitriol - CuSO₄.5H₂O

(i) Aqueous solution:
a) The solution in which water acts as a solvent is called aqueous solution.
b) Example: common salt in water, Copper Sulphate in water.
(ii) Non - Aqueous solution:
a) The solution in which any liquid, other than water, acts as a solvent is called non-aqueous solution.
b) Example: Sulphur dissolved in carbon disulphide, Iodine dissolved in carbon tetrachloride

i) Gas in liquid - CO₂ dissolved in water (Soda water)
ii) Solid in liquid - NaCl dissolved in water
iii) Solid in solid - Copper dissolved in gold (Alloys)
iv) Gas in gas - Mixture of Helium-oxygen gases

(i) A solution is a homogeneous mixture of two or more substances.
E g: Sea water.
(ii) In a solution, the component present in lesser amount by weight is called a solute.
(iii) The component present in a larger amount by weight is called a solvent.
(iv) Solute + Solvent → Solution

Given, Volume of ethanol = 3.5 lit
Volume of aqueous ethanol solution = 15 lit
Volume percent ethanol solution = ?
Volume percentage = \(\frac {Volume \ of \ the \ solute}{Volume \ of \ the \ solution}\) x 100
= \(\frac{3.5}{15}\times 100=\frac{350}{15}\) 
Volume percentage of ethanol solution = 23.33%

(i) Saturated solution:
a) A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature is called saturated solution.
b) E.g. 36 g of sodium chloride in 100 g of water at 25° C forms saturated solution.
c) Further addition of sodium chloride, leaves it undissolved.
(ii) Unsaturated solution:
a) Unsaturated solution is one that contains less solute than that of the saturated solution at a given temperature.
b) E.g. 10 g or 20 g or 30 g of Sodium chloride in 100 g of water at 25°C forms an unsaturated solution.

(i) Cool drinks give more fizz at the foot of mountain because the atmospheric pressure is less at the top of the mountain.
(ii) So the pressure affects the fizz of the cool drink.