Assertion (A): An inoculum of curd is used for curdling of milk. Reason (R): It contains Lactobacillus, which improves nutritional quality by increasing Vitamin `B_(12)`

Options

A. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
B. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason (R) is false.
D. Assertion (A) is false but reason (R) is true.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that an inoculum of curd is used for curdling milk. This means that when we add curd (which contains live bacteria) to milk, it helps in the process of turning milk into curd.

**Hint**: Think about what happens when you add curd to milk. What process does it initiate?

2. **Understanding the Reason**: The reason given is that the inoculum contains Lactobacillus, a type of bacteria that is known to improve the nutritional quality of the curd by increasing Vitamin B12 levels. Lactobacillus is a key player in the fermentation process.

**Hint**: Recall the role of Lactobacillus in dairy products. What benefits does it provide?

3. **Evaluating the Assertion and Reason**: Both the assertion and reason are true. The inoculum of curd does indeed help in curdling milk, and Lactobacillus does contribute to the nutritional enhancement of the curd, including the production of Vitamin B12.

**Hint**: Consider if both statements are factual and if one logically supports the other.

4. **Conclusion**: Since both the assertion and reason are correct and the reason explains the assertion, the correct answer is that both are correct and the reason provides a correct explanation for the assertion.

**Hint**: Look for options that state both are correct and that one explains the other.

### Final Answer:
The correct option is that both the assertion and reason are correct, and the reason provides a correct explanation for the assertion.