Which is not a colloidal solution?

Solution:

A colloidal solution is a heterogeneous system in which one substance is dispersed as very fine particles (ranging from 1 nm to 1000 nm) in another substance called the dispersion medium.

Let's analyze the given options:

1. Air: Air is a homogeneous mixture of various gases (like nitrogen, oxygen, argon, carbon dioxide, etc.). The components are mixed at a molecular level, forming a true solution, not a colloidal solution.

2. Milk: Milk is an emulsion, which is a type of colloid where the dispersed phase (fat globules) and the dispersion medium (water) are both liquids.

3. Smoke: Smoke is an aerosol, a type of colloid where solid particles (like carbon) are dispersed in a gas (air).

4. Blood: Blood is a complex biological fluid that contains various components like proteins, cells, and platelets dispersed in plasma, making it a colloidal system.

Therefore, Air is not a colloidal solution.