Rodenticides are

Options

A. chemicals used to kill insects
B. chemicals used to kill rats
C. high quality fertilisers
D. chemicals used to kill persistent weeds.

Explanation

### Step-by-Step Solution:

1. **Definition of Rodenticides**: Rodenticides are chemical substances specifically designed to kill rodents, which include animals like rats and mice.

2. **Purpose of Rodenticides**: These chemicals are used primarily in agricultural settings to protect crops from damage caused by rodent infestations. Rodents can cause significant harm to crops, leading to economic losses for farmers.

3. **Specificity of Rodenticides**: Rodenticides are formulated to target only rodents, meaning they are designed to kill rats and mice while not harming the crops themselves. This specificity is crucial for maintaining the health of the agricultural ecosystem.

4. **Comparison with Other Chemicals**:
- Insecticides are chemicals used to kill insects, not rodents.
- Herbicides (or weedicides) are used to kill weeds, which are unwanted plants, and are not related to rodenticides.

5. **Conclusion**: The correct identification of rodenticides is that they are chemicals used to kill rodents, specifically rats and mice, and are distinct from other agricultural chemicals like insecticides and herbicides.