Volume of the ethanol = 35 ml
Volume of the water = 65 ml
Volume percentage = \(\frac{\text { Volume of the solute }}{\text { Volume of the solution }} \times 100\)
Volume percentage =\(\frac{\text { Volume of the solute }}{\text { Volume of the solute + Volume of the solvent }} \times 100\) 
Volume percentage = \(\frac{35}{35+65}\times\)100
Volume percentage = \(\frac{35}{100 }\) x 100
= 35%

a) MgSO₄.7H₂O is heating process:
(i) Magnesium Sulphate heptahydrate or Epsom salt MgSO₄.7H₂O water of crystallization is 7.
(ii) When magnesium sulphate heptahydrate crystals are gently heated, it loses seven water molecules, and becomes anhydrous magnesium sulphate.

(iii) If you add few drops of water or allow it to cool, the colourless anhydrous salt again turns back into hydrated salt.
b) Solubility:
b) Solubility is defined as the number of grams of a solute that can be dissolved in 100g of a solvent to form its saturated solution at a given temperature and pressure.
Solubility = \(\frac{Mass \ of \ the \ solute}{Mass \ of \ the \ solvent}\) x 100

There are three main factors which govern the solubility of a solute. They are:
a) Nature of the solute and solvent
b) Temperature
c) Pressure
a) Nature of the solute and solvent:
(i) The nature of the solute and solvent plays an important role in solubility.
(ii) Although water dissolves an enormous variety of substances, both ionic and covalent, it does not dissolve everything.
(iii) The phrase that scientists often use when predicting solubility is "like dissolves like".
(iv) The expression means that dissolving occurs when similarities exist between the solvent and the solute.
(v) For example: Common salt is a polar compound 4 and dissolves readily in polar solvent like water.
(vi) Non-polar compounds are soluble in non-polar solvents. For example: Fat dissolved in ether.
(vii) But non-polar compounds, do not dissolve in polar solvents; polar compounds do not dissolve in non-polar solvents.
b) Effect of Temperature:
Solubility of Solids in Liquid:
(i) Generally, solubility of a solid solute in a liquid solvent increases with increase in temperature.
(ii) For example, a greater amount of sugar will dissolve in warm water than in cold water.
(iii) In endothermic process, solubility increases with increase in temperature.
(iv) In exothermic process, solubility decreases with increase in temperature.
Solubility of Gases in liquid:
(i) Solubility of gases in liquid decrease with increase in temperature.
(ii) Generally, water contains dissolved oxygen.
(iii) When water is boiled, the solubility of oxygen in water decreases, so oxygen escapes in the form of bubbles.
(iv) Aquatic animals live more in cold regions because, more amount of dissolved oxygen is present in the water of cold regions.
(v) This shows that the solubility of oxygen in water is more at low temperatures.
c) Effect of Pressure:
(i) Effect of pressure is observed only in the case of solubility of a gas in a liquid.
(ii) When the pressure is increased, the solubility of a gas in liquid increases.
(iii) The common examples for solubility of gases in liquids are carbonated beverages, i.e. soft drinks, household cleaners containing aqueous solution of ammonia, formalin aqueous solution of formaldehyde, etc.

(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.

(i) 'A' is copper sulphate pentahydrate (CuSO₄.5H₂O).
(ii) 'B' is Anhydrous copper sulphate (CuSO₄)

When ionic substances are dissolved in water to make their saturated aqueous solution, their ions attract water molecules which then attached chemically in certain ratio. This process is called hydration.

Two solutes are dissolved in one solvent. Such kind of solutions which contain three components are called trinary solutions.

Concentration of a solution
= \(\frac{Amount \ of \ the \ solute}{Amount \ of \ solvent }\) x 100
= \(\frac{20}{40}\) x 100
= 50