Assertion : Excess nitrate in drinking water causes 'blue baby' syndrome.
Reason : The maximum limit of nitrate in drinking water is 50 ppb.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the c orrect explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To solve the assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
The assertion states that "Excess nitrate in drinking water causes 'blue baby' syndrome."

- **Explanation:**
- Nitrate (NO3-) can be converted into nitrite (NO2-) in the human body. When infants consume water with high levels of nitrate, the nitrite can react with hemoglobin in their blood to form methemoglobin.
- Methemoglobin cannot effectively carry oxygen, leading to a condition where the blood is unable to transport sufficient oxygen to the body's tissues. This results in a bluish discoloration of the skin, particularly noticeable in the veins of babies, hence the name "blue baby syndrome."

### Step 2: Analyze the Reason
The reason states that "The maximum limit of nitrate in drinking water is 50 ppb."

- **Explanation:**
- The maximum permissible limit of nitrate in drinking water is actually 50 parts per million (ppm), not parts per billion (ppb).
- 1 ppm is equivalent to 1000 ppb, which means that the correct limit is significantly higher than what is stated in the reason.

### Step 3: Conclusion
- The assertion is **true** because excess nitrate does indeed cause blue baby syndrome.
- The reason is **false** because the maximum limit of nitrate in drinking water is 50 ppm, not 50 ppb.

### Final Answer
- Therefore, the correct conclusion is that the assertion is true, and the reason is false.