An inborn error of metabolism which eventually affects mental development is

Options

A. Albinism
B. Phenylketonuria
C. Anaemia
D. Bleeder's disease

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for an inborn error of metabolism that affects mental development. Inborn errors of metabolism are genetic disorders that result from a deficiency in a specific enzyme, leading to the accumulation of toxic substances in the body.

2. **Analyzing the Options**:
- **Albinism**: This condition is characterized by a lack of melanin production, affecting skin and eye color, but it does not primarily affect mental development.
- **Phenylketonuria (PKU)**: This is an inherited disorder that results in the inability to metabolize the amino acid phenylalanine due to a deficiency in the enzyme phenylalanine hydroxylase. If untreated, it can lead to severe intellectual disability and other mental health issues.
- **Anemia**: This condition refers to a deficiency of red blood cells or hemoglobin, which primarily affects oxygen transport in the body and does not directly impact mental development.
- **Bleeder's Disease (Hemophilia)**: This is a blood clotting disorder caused by a deficiency in clotting factors, which does not relate to metabolism or mental development.

3. **Identifying the Correct Answer**: Given the analysis of the options, phenylketonuria (PKU) is the only condition that is an inborn error of metabolism and has a direct impact on mental development if left untreated.

4. **Conclusion**: The correct answer to the question is **Phenylketonuria**.