The correct answer is option 'C' - Apocarpous.

Explanation:
An ovary is a part of the female reproductive system in plants. It is a hollow structure located at the base of the carpel. A carpel is the female reproductive organ of a flower and is composed of three parts: the stigma, style, and ovary.

In the case of a single free carpel, the ovary is called apocarpous. Apocarpous means that the carpel is composed of separate, distinct, and free units. Each unit has its own ovary, style, and stigma. These units are known as simple pistils.

The term "apocarpous" can be broken down to understand its meaning:

1. "Apo-" means separate or distinct.
2. "-carpous" refers to the carpel, which is the female reproductive organ of a flower.

Characteristics of an apocarpous ovary:

1. Single free carpel: The ovary is not fused with other carpels and remains separate.
2. Multiple units: The ovary consists of multiple separate units, each with its own ovule(s).
3. Independent development: Each unit develops independently and can form separate fruits after fertilization.
4. Differentiation: The carpels can be differentiated based on the number of units present in the ovary. For example, a gynoecium with five apocarpous carpels would be called pentacarpellary.

Example:
A good example of an apocarpous ovary is found in the buttercup flower (Ranunculus). The buttercup has several separate carpels, each with its own ovary. After fertilization, each ovary develops into a separate fruit called an achene.

In conclusion, an ovary belonging to a single free carpel is called apocarpous. This term describes the condition where the carpel is composed of separate and distinct units, each with its own ovary.