The most abundant prokaryotes helpful to humans in making curd from milk and in production of antibiotics are the ones categorised as

Options

A. Chemosynthetic autotrophs
B. Heterotrophic bacteria
C. Cyanobacteria
D. Archaebacteria

Answer

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the type of prokaryotes that are most abundant and are helpful to humans in making curd from milk and in the production of antibiotics.

2. **Identify the Options**: The options provided are:
- A) Chemosynthetic autotrophs
- B) Heterotrophic bacteria
- C) Cyanobacteria
- D) Archaebacteria

3. **Analyze Each Option**:
- **Option A: Chemosynthetic Autotrophs**: These organisms produce their own energy from inorganic substances. They are not involved in the production of curd or antibiotics. Therefore, this option is incorrect.

- **Option B: Heterotrophic Bacteria**: These bacteria depend on other organisms for their energy and nutrients. They play a crucial role in the fermentation process, which is essential for making curd from milk. Additionally, many heterotrophic bacteria are known for their ability to produce antibiotics. This makes this option a strong candidate.

- **Option C: Cyanobacteria**: These are photosynthetic bacteria (often referred to as blue-green algae) that are primarily involved in nitrogen fixation and are considered biofertilizers. They do not contribute to curd production or antibiotic synthesis, making this option incorrect.

- **Option D: Archaebacteria**: This group of prokaryotes is distinct from bacteria and is known for living in extreme environments. They do not have significant roles in curd production or antibiotic production, thus this option is also incorrect.

4. **Conclusion**: After analyzing all options, the correct answer is **Option B: Heterotrophic Bacteria**. These are the prokaryotes that are most abundant and helpful in making curd from milk and in the production of antibiotics.

### Final Answer:
**Heterotrophic bacteria (Option B)**

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