NCERT Class 8 Science Chapter 9

A solution is a homogeneous mixture of a solute and a solvent. The solute is the substance that dissolves (e.g., sugar) and is present in smaller amounts. The solvent is the substance that dissolves the solute (e.g., water) and is present in larger amounts. When sugar is dissolved in water, sugar is the solute and water is the solvent.

Solubility is affected by: (1) Temperature — solubility of most solids increases with temperature; solubility of gases decreases with temperature. (2) Nature of solute and solvent — 'like dissolves like' (polar in polar, non-polar in non-polar). (3) Pressure — mainly affects gas solubility; higher pressure increases gas solubility (e.g., CO₂ in carbonated drinks).

A saturated solution holds the maximum amount of dissolved solute at a given temperature — no more solute can dissolve. An unsaturated solution can still dissolve more solute. A supersaturated solution holds more solute than normal by being carefully cooled or handled.

Concentration refers to how much solute is dissolved in a given amount of solvent or solution. A concentrated solution has a large amount of solute, while a dilute solution has a small amount. Concentration can be expressed as: mass of solute per volume of solution (g/L) or as a percentage.

Yes, air is a solution (a gaseous solution). It is a homogeneous mixture of gases — primarily nitrogen (about 78%), oxygen (about 21%), argon, carbon dioxide, and other trace gases. The main solvent is nitrogen and all other gases are dissolved in it. NCERT Class 8 Chapter 9 discusses various types of solutions.

At higher temperatures, water molecules move faster and have more energy to break apart the sugar molecules and surround them. This increases the solubility of sugar in hot water compared to cold water. This is why tea or coffee tastes better when you add sugar while the liquid is still hot.