Kinematic viscosity is a fundamental property of fluids that describes its resistance to flow. It is defined as the ratio of the absolute viscosity (also known as dynamic viscosity) of a fluid to its density. The correct answer is option 'A', which states that kinematic viscosity is the ratio of absolute viscosity to the density of the liquid. Let's break down this answer and explain it in detail.

Heading 1: What is kinematic viscosity?
- Kinematic viscosity is a measure of the internal friction or resistance to flow within a fluid.
- It is a property of the fluid that determines how easily it flows under the influence of an applied force.
- It is denoted by the symbol 'ν' and is measured in units of square meters per second (m²/s).

Heading 2: Absolute viscosity
- Absolute viscosity, also known as dynamic viscosity, is a measure of the internal friction within a fluid due to the cohesive forces between its molecules.
- It is a measure of the fluid's resistance to shear or deformation.
- Absolute viscosity is denoted by the symbol 'η' and is measured in units of pascal-seconds (Pa·s) or poise (P).

Heading 3: Density of the liquid
- Density is defined as the mass per unit volume of a substance.
- It is a measure of how closely packed the particles of a substance are.
- Density is denoted by the symbol 'ρ' and is measured in units of kilograms per cubic meter (kg/m³).

Heading 4: Relationship between kinematic viscosity, absolute viscosity, and density
- Kinematic viscosity is defined as the ratio of absolute viscosity to the density of the liquid.
- Mathematically, kinematic viscosity (ν) can be expressed as:
ν = η / ρ
- This equation shows that the kinematic viscosity is directly proportional to the absolute viscosity and inversely proportional to the density of the liquid.
- In simpler terms, the kinematic viscosity of a fluid increases with an increase in absolute viscosity or a decrease in density.

Heading 5: Importance of kinematic viscosity
- Kinematic viscosity is an important property in various fields such as fluid mechanics, engineering, and geophysics.
- It helps in characterizing the flow behavior of fluids, predicting their resistance to flow, and understanding fluid dynamics.
- It is also used in the design and optimization of hydraulic systems, lubrication processes, and fluid flow simulations.

In conclusion, kinematic viscosity is the ratio of absolute viscosity to the density of a liquid. It is a fundamental property that describes the resistance to flow of a fluid and is widely used in various applications.