Q1: Force between the molecules of the same substance is called __________ force.

ANS:B - cohesive

Cohesive refers to the ability of particles or molecules of the same substance to stick together or be attracted to each other. In the context of materials science and chemistry, cohesive interactions are fundamental to understanding the behavior of substances. Cohesive forces arise from various interactions between molecules, such as:

1. Van der Waals Forces: These are weak intermolecular forces that arise from temporary or induced dipoles in molecules. Van der Waals forces include London dispersion forces and dipole-dipole interactions.
2. Hydrogen Bonding: A special type of dipole-dipole interaction that occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine). Hydrogen bonding is stronger than typical van der Waals forces.
3. Ionic Interactions: In ionic compounds, such as salts, positively and negatively charged ions are held together by strong electrostatic forces of attraction.
4. Covalent Bonds: In some cases, cohesive forces can arise from the sharing of electrons between atoms in covalent bonds. This is particularly relevant in macromolecules such as polymers.

The cohesive forces within a substance determine its physical properties such as:

• Viscosity: The resistance of a fluid to flow is influenced by cohesive forces between its molecules. Stronger cohesive forces generally result in higher viscosity.
• Surface Tension: The cohesive forces between liquid molecules at the surface of a liquid cause it to minimize its surface area, resulting in surface tension. This property allows some insects, for example, to walk on water.
• Melting and Boiling Points: The strength of cohesive forces affects the temperature at which a substance changes from solid to liquid (melting point) and from liquid to gas (boiling point).

Understanding cohesive interactions is essential in various fields, including materials science, chemistry, and biology, as they govern the behavior and properties of substances at the molecular level.