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

Options

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

Answer

To solve the question regarding the most abundant prokaryotes that are helpful to humans in making curd and in the production of antibiotics, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify which category of prokaryotes is most abundant and beneficial for making curd and producing antibiotics.

2. **Analyze the Options**:
- **Option 1: Archaebacteria**: These are known as extremophiles and thrive in extreme environments. They are not involved in curd making or antibiotic production.
- **Option 2: Chemosynthetic Autotrophs**: These organisms derive energy from the oxidation of inorganic substances. They are not involved in curd making or antibiotic production.
- **Option 3: Heterotrophic Bacteria**: These bacteria derive energy from organic carbon sources. They play a significant role in food production, including curd making, and are also involved in the production of antibiotics.
- **Option 4: Cyanobacteria**: Known as blue-green algae, they are primarily involved in nitrogen fixation and photosynthesis, but they do not contribute to curd making or antibiotic production.

3. **Identify the Correct Option**: Based on the analysis, the only category that is helpful in both making curd and producing antibiotics is **Heterotrophic Bacteria**.

4. **Conclusion**: Therefore, the correct answer is **Option 3: Heterotrophic Bacteria**.

### Final Answer:
The most abundant prokaryotes helpful to humans in making curd and in the production of antibiotics are categorized as **Heterotrophic Bacteria**.

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