Q1: Surface tension of a liquid

ANS:D - all (a), (b) & (c).

(a) Surface tension of a liquid is due to intermolecular forces of cohesion. Explanation:

• Surface tension is indeed due to the intermolecular forces of cohesion. Cohesion refers to the attraction between molecules of the same substance. At the surface of a liquid, molecules experience stronger cohesive forces with neighboring molecules in the liquid than with molecules in the surrounding medium (e.g., air). This imbalance in forces results in a net inward force, which creates the phenomenon known as surface tension. In summary, surface tension arises due to the cohesive forces between molecules within the liquid.

(b) Decreases with rise in temperature. Explanation:

• Surface tension typically decreases with an increase in temperature. This is because higher temperatures lead to increased molecular motion and kinetic energy within the liquid. As the temperature rises, molecules at the surface of the liquid gain more kinetic energy, making it easier for them to overcome the cohesive forces holding them together. As a result, the surface tension decreases, and the liquid's surface becomes less "tense" or resistant to deformation. Conversely, at lower temperatures, surface tension tends to increase due to reduced molecular motion and stronger cohesive forces.

(c) Is responsible for the spherical shape of an isolated liquid drop. Explanation:

• Surface tension is indeed responsible for the spherical shape of an isolated liquid drop. When a liquid drop is isolated (i.e., not in contact with any other surface), the cohesive forces between molecules within the drop cause it to minimize its surface area to reduce the surface energy. The shape that minimizes the surface area for a given volume is a sphere. The surface tension acts as an inward force, pulling the molecules at the surface of the drop inward, resulting in a spherical shape. This phenomenon is commonly observed in liquid droplets formed by condensation, or when small volumes of liquid are released from a nozzle or pipette.

In summary, all three statements are correct because they accurately describe different aspects of surface tension and its effects on liquids. Surface tension arises from cohesive forces between molecules within the liquid, tends to decrease with increasing temperature, and is responsible for the spherical shape of isolated liquid drops.