Productivity is the rate of production of biomass expressed in terms of:
`{:(i.("kcal m"^(-3))yr^(-1),,,ii.g^(-2)yr^(-1)),(iii.g^(-1)yr^(-1),,,iv. ("kcal m"^(-2))yr^(-1)):}`

Options

A. ii
B. iii
C. I and ii
D. ii and iv

Answer

To determine the correct expression for productivity in terms of biomass, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Productivity**: Productivity refers to the rate at which biomass is produced in an ecosystem. Biomass is the total mass of living matter in a given area.

2. **Units of Measurement**: Productivity can be expressed in two main ways:
- **Weight**: This is often measured in grams (g) per unit area (m²) per year (yr).
- **Energy**: This can be measured in kilocalories (kcal) per unit area (m²) per year (yr).

3. **Analyzing the Options**: The options provided are:
- (i) kcal m^(-3) yr^(-1)
- (ii) g m^(-2) yr^(-1)
- (iii) g^(-1) yr^(-1)
- (iv) kcal m^(-2) yr^(-1)

4. **Identifying the Correct Units**:
- Option (i) kcal m^(-3) yr^(-1): This measures energy per volume, which is not suitable for productivity.
- Option (ii) g m^(-2) yr^(-1): This measures biomass per area per year, which is a valid expression for productivity.
- Option (iii) g^(-1) yr^(-1): This is not a standard way to express productivity.
- Option (iv) kcal m^(-2) yr^(-1): This measures energy per area per year, which is also a valid expression for productivity.

5. **Conclusion**: The correct expressions for productivity in terms of biomass are:
- Option (ii) g m^(-2) yr^(-1) (weight-based)
- Option (iv) kcal m^(-2) yr^(-1) (energy-based)

Thus, the correct answers are options (ii) and (iv).

### Final Answer:
The rate of production of biomass (productivity) can be expressed in terms of:
- (ii) g m^(-2) yr^(-1)
- (iv) kcal m^(-2) yr^(-1)