The heats of neutralisation of `CH_3COOH, HCOOH, HCN and H_2S` are - 13.2, - 13.4, -2.9 and - 3.8 kCal per equivalent respectively. Arrange the acids in increasing order of acidic strength.

Options

A. `HCOOH gt CH_3COOH gt H_2S gt HCN`
B. `CH_3COOH gt HCOOH gt H_2S gt HCN`
C. `H_2S gt HCOOH gt CH_3COOH gt HCN`
D. `HCOOH gt H_2S gt CH_3COOH gt HCN`

Answer

To determine the increasing order of acidic strength among the given acids based on their heats of neutralization, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Heat of Neutralization**:
- The heat of neutralization is the heat released when an acid reacts with a base to form water and a salt. Stronger acids release more heat during neutralization because they dissociate more completely in solution.

2. **List the Given Heats of Neutralization**:
- The heats of neutralization for the acids are:
- Acetic acid (CH₃COOH): -13.2 kCal/equiv
- Formic acid (HCOOH): -13.4 kCal/equiv
- Hydrocyanic acid (HCN): -2.9 kCal/equiv
- Hydrogen sulfide (H₂S): -3.8 kCal/equiv

3. **Identify the Most Negative Heat Values**:
- The more negative the heat of neutralization, the stronger the acid. We will compare the values:
- HCOOH: -13.4 kCal/equiv (most negative)
- CH₃COOH: -13.2 kCal/equiv
- H₂S: -3.8 kCal/equiv
- HCN: -2.9 kCal/equiv (least negative)

4. **Rank the Acids Based on Their Heats of Neutralization**:
- From the most negative to the least negative:
1. HCOOH (-13.4 kCal/equiv) - strongest acid
2. CH₃COOH (-13.2 kCal/equiv)
3. H₂S (-3.8 kCal/equiv)
4. HCN (-2.9 kCal/equiv) - weakest acid

5. **Write the Final Order**:
- The increasing order of acidic strength is:
- HCN < H₂S < CH₃COOH < HCOOH

### Final Answer:
The acids arranged in increasing order of acidic strength are:
**HCN < H₂S < CH₃COOH < HCOOH**