The heats of neutralisation of four acids `a`, `b`, `c` and `d` when neutralised against a common base are `13.7`, `9.4`, `11.2` and `12.4` kcal respectively. The weakest among these acids is

Options

A. A
B. B
C. C
D. D

Answer

To determine the weakest acid among the four given acids based on their heats of neutralization, we can follow these steps:

### Step 1: Understand the concept of heat of neutralization
The heat of neutralization is the amount of heat released when an acid reacts with a base to form water and a salt. Generally, stronger acids release more heat during neutralization because they ionize completely in solution, providing more H⁺ ions.

### Step 2: List the heats of neutralization for each acid
The heats of neutralization for the acids are given as follows:
- Acid A: 13.7 kcal
- Acid B: 9.4 kcal
- Acid C: 11.2 kcal
- Acid D: 12.4 kcal

### Step 3: Compare the heats of neutralization
To find the weakest acid, we need to identify which acid has the lowest heat of neutralization. The values are:
- A: 13.7 kcal
- B: 9.4 kcal
- C: 11.2 kcal
- D: 12.4 kcal

### Step 4: Identify the lowest value
From the listed heats of neutralization, we can see that:
- Acid B has the lowest heat of neutralization at 9.4 kcal.

### Step 5: Conclusion
Since the heat of neutralization is inversely related to the strength of the acid, the acid with the lowest heat of neutralization (Acid B) is the weakest acid among the four.

### Final Answer
The weakest acid among the given acids is **Acid B**.

---