(a) It is said th

(a) Molecules of many elements, such as argon (Ar), helium (He), neon (Ne), etc., are made up of only one atom of the element because:

i. These elements are noble gases that are unreactive in nature.

ii. They have completely filled outermost shells.

iii. As a result, they are unable to combine with any other element.

iv. Hence, they exist independently in the form of a single atom.

(b) Difference between ion and atom may be encountered as:

OR

a) Solvent dissolves solute particles by overcoming the intermolecular forces between the solute (or one can call it the solute-solute interaction). So, to dissolve a solute, the solute-solute interaction must be broken by the solvent particles.

When the temperature increases, the kinetic energy of the solvent particles increases, causing to break the solute-solute interactions more effectively. This allows the addition of more solute particles, as there is space to accommodate more solute particles. So the solubility increases with an increase in temperature. Lowering the temperature does the opposite. It decreases the solubility of the solute.

(b) The phenomenon where the path of the light beam is visible as a result of scattering of light by colloidal particles is called the Tyndall effect. The size of the particle should be such that it should scatter light. Particles that are very small (in the case of true solutions) or very large (in the case of suspensions) do not scatter light. So, the Tyndall effect is not observed in true solutions or suspensions.

This is the general case. In certain special cases, if the particle size of suspension is small enough to scatter light, then suspensions also show the Tyndall effect.

(c) Cream and milk differ in their density. The cream is denser than milk. When milk is churned (shaking or spinning of a container containing milk by applying a rotating force) the denser particles (cream) tend to remain at the bottom, whereas the lighter particles (milk) stay at the top, along with the direction of spin. This process is called centrifugation.