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. ii and iv
D. I and iii

Explanation

To solve the question regarding the units of productivity in terms of biomass production, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Productivity**:
- Productivity refers to the rate of biomass production in an ecosystem. It can be expressed in terms of energy (like kilocalories) or mass (like grams).

2. **Identifying the Units**:
- The question provides four different units:
- (i) `kcal m^(-3) yr^(-1)`
- (ii) `g m^(-2) yr^(-1)`
- (iii) `g m^(-1) yr^(-1)`
- (iv) `kcal m^(-2) yr^(-1)`

3. **Analyzing Each Unit**:
- **(i) `kcal m^(-3) yr^(-1)`**: This unit suggests energy per volume (cubic meter), which is not typically used for productivity.
- **(ii) `g m^(-2) yr^(-1)`**: This unit indicates grams per area (square meter) per year, which is a valid measure of biomass production.
- **(iii) `g m^(-1) yr^(-1)`**: This unit indicates grams per linear meter per year, which is not a standard measure for productivity.
- **(iv) `kcal m^(-2) yr^(-1)`**: This unit indicates energy (in kilocalories) per area (square meter) per year, which is also a valid measure of productivity.

4. **Selecting the Correct Units**:
- From the analysis, the valid units for expressing productivity are:
- (ii) `g m^(-2) yr^(-1)`
- (iv) `kcal m^(-2) yr^(-1)`

5. **Conclusion**:
- The correct options for expressing productivity in terms of biomass production are (ii) and (iv). Therefore, the answer is option 2, which corresponds to the valid units for productivity.

### Final Answer:
The correct units for expressing productivity are:
- (ii) `g m^(-2) yr^(-1)`
- (iv) `kcal m^(-2) yr^(-1)`