According to CIP rule, the correct arrangment in order of decreasing priority is :-

Options

A. `–OH gt –CH_(2)OH gt –CHO gt –COOH `
B. `–OH gt –COOH gt –CHO gt –CH_2OH `
C. `–COOH gt –OH gt –CHO gt –CH_(2)OH `
D. `–COOH gt –CHO gt –CH_(2)OH gt –OH`

Answer

To determine the correct arrangement of the given groups (OH, CH2OH, CHO, and COOH) in order of decreasing priority according to the Cahn-Ingold-Prelog (CIP) priority rules, we follow these steps:

### Step 1: Identify the Atoms in Each Group
- **OH**: Contains O (oxygen) and H (hydrogen).
- **CH2OH**: Contains C (carbon), O (oxygen), and H (hydrogens).
- **CHO**: Contains C (carbon) and O (oxygen).
- **COOH**: Contains C (carbon), O (oxygen), and H (hydrogen).

### Step 2: Assign Atomic Numbers
Using the atomic numbers of the atoms:
- O (oxygen) = 8
- C (carbon) = 6
- H (hydrogen) = 1

### Step 3: Compare the First Atoms
- **OH**: The first atom is O (atomic number 8).
- **CH2OH**: The first atom is C (atomic number 6).
- **CHO**: The first atom is C (atomic number 6).
- **COOH**: The first atom is C (atomic number 6).

Since OH has oxygen as the first atom, it has the highest priority.

### Step 4: Compare the Remaining Groups
Now we compare the remaining groups (CH2OH, CHO, COOH):
- **COOH**: The first atom is C, but it has two O atoms (one in the carboxylic group).
- **CHO**: The first atom is C, with one O atom.
- **CH2OH**: The first atom is C, with one O atom.

### Step 5: Determine the Next Highest Priority
- COOH has the highest priority among CH2OH and CHO due to the presence of the carboxylic group (COOH).
- Between CH2OH and CHO, CHO has a higher priority because it has an O atom directly bonded to the carbon, while CH2OH has two H atoms bonded to the carbon.

### Final Order of Decreasing Priority
1. **OH** (highest priority)
2. **COOH**
3. **CHO**
4. **CH2OH** (lowest priority)

### Conclusion
The correct arrangement in order of decreasing priority is:
**OH > COOH > CHO > CH2OH**