Assertion: Smaller the organism, higher is the rate of metabolism per gram weight.
Reason: The heart rate of a six months old baby is much higher than that of adult.

Options

A. (a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion, then mark a.
B. (b) If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion, then mark b.
C. (c) If Assertion is true statement but Reason is false, then mark c.
D. (d) If both Assertion and Reason are false statements then mark d.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states: "Smaller the organism, higher is the rate of metabolism per gram weight."

- **Explanation**: The metabolic rate, specifically the Basal Metabolic Rate (BMR), is inversely proportional to the weight of the organism. This means that smaller organisms tend to have a higher metabolic rate per gram of body weight compared to larger organisms. For example, a mouse has a higher metabolic rate per gram than an elephant. Therefore, this assertion is correct.

### Step 2: Analyze the Reason
The reason states: "The heart rate of a six months old baby is much higher than that of an adult."

- **Explanation**: It is true that the heart rate of a six-month-old baby is significantly higher than that of an adult. A typical heart rate for a six-month-old baby ranges from 110 to 112 beats per minute, while an adult's heart rate is around 72 to 75 beats per minute. Thus, this reason is also correct.

### Step 3: Determine the Relationship
Now, we need to determine if the reason provided is a correct explanation for the assertion.

- **Analysis**: While both statements are true, the reason regarding heart rate does not explain why smaller organisms have a higher metabolic rate per gram weight. The metabolic rate is influenced by factors such as body size and energy requirements, but heart rate differences between infants and adults do not directly relate to the metabolic rates of organisms of different sizes.

### Conclusion
Both the assertion and the reason are correct, but the reason is not the correct explanation for the assertion. Therefore, the answer is:

**Option B**: Both assertion and reason are true, but reason is not the correct explanation for assertion.

---