Explanation:
Physical quantities can be classified into two types: scalar quantities and vector quantities. Scalar quantities have only magnitude while vector quantities have both magnitude and direction. Units are used to measure the magnitude of physical quantities while dimensions are used to describe the nature of physical quantities.

Relative velocity, angle, and energy are all physical quantities that have both units and dimensions.

Relative velocity:
- Velocity is a vector quantity that has both magnitude (speed) and direction.
- Relative velocity is the velocity of an object with respect to another object.
- It is measured in units of distance per unit time (e.g. meters per second) and has dimensions of length divided by time (e.g. [L]/[T]).

Angle:
- An angle is a measure of the separation between two lines or planes.
- It is a scalar quantity that only has magnitude and no direction.
- Angles are measured in units of radians or degrees and have no dimensions.

Energy:
- Energy is a scalar quantity that is defined as the ability to do work.
- It has both units and dimensions depending on the system of units used.
- In SI units, energy is measured in joules (J) and has dimensions of mass times length squared divided by time squared (e.g. [M][L]^2/[T]^2).

Relative density:
- Density is a scalar quantity that is defined as the mass per unit volume of a substance.
- Relative density is the ratio of the density of a substance to the density of a reference substance (usually water).
- It is a dimensionless quantity that has no units or dimensions.

Therefore, option B (Relative density) is the correct answer.