The decreasing basic character of the following is :
(I) `Ph O^(Ө)`
(II) `CH_3 S^(Ө)`
(III) `overset (Ө) O H`
(IV) `MeO^(Ө)`.

Options

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

Explanation

To determine the decreasing basic character of the given species (I) `Ph O^(−)`, (II) `CH_3 S^(−)`, (III) `O H^(−)`, and (IV) `MeO^(−)`, we can follow these steps:

### Step 1: Identify the Conjugate Acids
First, we need to identify the conjugate acids of the given bases:
- (I) `Ph O^(−)` → Conjugate acid is `Ph OH` (phenol)
- (II) `CH_3 S^(−)` → Conjugate acid is `CH_3 SH` (methanethiol)
- (III) `O H^(−)` → Conjugate acid is `H2O` (water)
- (IV) `MeO^(−)` → Conjugate acid is `MeOH` (methanol)

### Step 2: Determine the Acidity of the Conjugate Acids
Next, we need to determine the acidity of these conjugate acids. The stronger the acid, the weaker its conjugate base will be. The order of acidity based on known values is:
1. `Ph OH` (phenol) > 2. `CH_3 SH` (methanethiol) > 3. `MeOH` (methanol) > 4. `H2O` (water)

### Step 3: Relate Acidity to Basicity
Since the basicity is inversely related to acidity, we can derive the order of basicity from the order of acidity:
- The least acidic (strongest base) will be the most basic.
- The most acidic (weakest base) will be the least basic.

### Step 4: Write the Basicity Order
From the acidity order, we can conclude the basicity order as follows:
1. `O H^(−)` (from H2O) - strongest base
2. `MeO^(−)` (from MeOH)
3. `CH_3 S^(−)` (from CH_3 SH)
4. `Ph O^(−)` (from Ph OH) - weakest base

Thus, the decreasing basic character is:
**Basicity Order: `O H^(−) > MeO^(−) > CH_3 S^(−) > Ph O^(−)`**

### Final Answer
The decreasing basic character of the given species is:
**(III) `O H^(−)` > (IV) `MeO^(−)` > (II) `CH_3 S^(−)` > (I) `Ph O^(−)`**