The decreasing order of acidic character is `:`

Options

A. `(I)gt(II)gt(III)gt(IV)`
B. `(I)gt(II)gt(IV)gt(III)`
C. `(IV)gt(III)gt(II)gt(I)`
D. `(III)gt(IV)gt(II)gt(I)`

Answer

To determine the decreasing order of acidic character among the given compounds, we need to analyze the stability of their conjugate bases. The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**: Let's assume we are comparing the following compounds:
- CH3S-H (thioethanol)
- CH3O-H (methanol)
- CH3OH (methanol)
- H2O (water)
- C2H5OH (ethanol)

2. **Ionization and Conjugate Bases**: Each compound will ionize to produce an H+ ion and its corresponding conjugate base:
- CH3S-H → CH3S⁻ + H⁺
- CH3O-H → CH3O⁻ + H⁺
- CH3OH → CH3O⁻ + H⁺
- H2O → OH⁻ + H⁺
- C2H5OH → C2H5O⁻ + H⁺

3. **Stability of Conjugate Bases**:
- **CH3S⁻**: The sulfur atom can accommodate the negative charge due to its larger size and the presence of vacant 3d orbitals, making it more stable.
- **CH3O⁻**: Oxygen does not have vacant orbitals to stabilize the negative charge as effectively as sulfur, making it less stable than CH3S⁻.
- **OH⁻**: The negative charge on the hydroxide ion is relatively stable, but it is less stable than CH3S⁻.
- **C2H5O⁻**: Similar to CH3O⁻ but slightly less stable due to the larger alkyl group, which can destabilize the negative charge through inductive effects.
- **CH3OH**: Alcohols (except methanol) are generally less acidic than water, and thus CH3OH is less acidic than H2O.

4. **Comparing Acidity**:
- From the analysis, we can conclude:
- CH3S-H (most acidic)
- CH3O-H (more acidic than water)
- H2O (more acidic than ethanol)
- C2H5OH (least acidic)

5. **Final Order**: Therefore, the decreasing order of acidic character is:
- CH3S-H > CH3O-H > H2O > C2H5OH

### Final Answer:
The correct order of decreasing acidity is: **CH3S-H > CH3O-H > H2O > C2H5OH**.