Substance essential for absorption of vitamin `B_12` is

Options

A. Intrinsic factor
B. Pepsinogen
C. Prorennin
D. Enterokinase

Answer

### Step-by-Step Solution

1. **Identify the Question**: The question asks for the substance essential for the absorption of vitamin B12.

2. **Review the Options**: The options given are:
- A) Intrinsic factor
- B) Pepsinogen
- C) Prorenin
- D) Enterokinase

3. **Understand Vitamin B12 Absorption**: Vitamin B12 absorption occurs in the intestines and is dependent on certain factors.

4. **Role of Hydrochloric Acid (HCl)**: In the stomach, hydrochloric acid (HCl) separates vitamin B12 from the proteins it is bound to in food. This is the first step in the absorption process.

5. **Role of Intrinsic Factor**: After HCl separates vitamin B12 from proteins, it must bind to another protein produced in the stomach known as the intrinsic factor. This intrinsic factor is crucial for the absorption of vitamin B12 in the intestines.

6. **Conclusion**: The substance essential for the absorption of vitamin B12 is the intrinsic factor. Therefore, the correct answer is option A) Intrinsic factor.

### Final Answer
The substance essential for absorption of vitamin B12 is **intrinsic factor**.

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