Size of population is :

Options

A. Population density
B. Number of individuals per unit area
C. Represented by N
D. All of the above

Answer

### Step-by-Step Solution:

1. **Understanding Population Size**:
- The size of a population refers to the total number of individuals within a specific area at a given time.

2. **Defining Population Density**:
- Population density is a term that describes the number of individuals per unit area. It is a way to quantify how crowded a population is in a particular habitat.

3. **Symbol Representation**:
- Population density is often represented by the symbol "n". This symbol helps in mathematical calculations and ecological studies.

4. **Evaluating Population Changes**:
- Changes in population size or density can be used to assess various ecological processes, such as competition among species, resource availability, and environmental impacts.

5. **Conclusion**:
- Based on the definitions and explanations, we can conclude that the size of a population is indeed referred to as population density, which is represented by "n" and is defined as the number of individuals per unit area.

6. **Final Answer**:
- Therefore, the correct option regarding the size of the population is "all of the above".