Reactivity of `PhMgBr` with the following in the decreasing order is :
(i) Alcohol
(ii) Aldehyde
(iii) Ketone
(iv) Ester.

Options

A. `(iv) gt (iii) gt (ii) gt (i)`
B. `(i) gt (ii) gt (iii) gt (iv)`
C. `(ii) gt (iii) gt (i) gt (iv)`
D. `(iv) gt (i) gt (iii) gt (ii)`

Answer

To determine the reactivity of phenyl magnesium bromide (PhMgBr) with alcohols, aldehydes, ketones, and esters in decreasing order, we need to analyze the nature of each functional group and how they interact with Grignard reagents.

### Step-by-Step Solution:

1. **Understanding Grignard Reagents**:
- Grignard reagents, such as PhMgBr, are strong nucleophiles and bases. They react readily with electrophiles and can also deprotonate acidic hydrogens.

2. **Reactivity with Alcohols**:
- Alcohols contain an -OH group, where the hydrogen is attached to an electronegative oxygen atom. This hydrogen is acidic and can be easily deprotonated by Grignard reagents.
- Therefore, alcohols are highly reactive with Grignard reagents.

3. **Reactivity with Aldehydes**:
- Aldehydes have a carbonyl group (C=O) with one hydrogen atom attached to the carbon. They are less sterically hindered compared to ketones, making them more reactive than ketones.
- Aldehydes can undergo nucleophilic addition with Grignard reagents, leading to the formation of alcohols.

4. **Reactivity with Ketones**:
- Ketones also contain a carbonyl group but have two alkyl groups attached to the carbon. These alkyl groups can donate electron density, making the carbonyl carbon less electrophilic compared to aldehydes.
- Thus, ketones are less reactive than aldehydes but more reactive than esters.

5. **Reactivity with Esters**:
- Esters have a carbonyl group as well, but they also have an alkoxy group (R-O) attached. The alkoxy group is an electron-donating group, which decreases the electrophilicity of the carbonyl carbon.
- Consequently, esters are the least reactive towards Grignard reagents.

### Final Order of Reactivity:
Based on the above analysis, the decreasing order of reactivity of PhMgBr with the given compounds is:
1. Alcohol (most reactive)
2. Aldehyde
3. Ketone
4. Ester (least reactive)

### Answer:
The reactivity of PhMgBr in decreasing order is: **Alcohol > Aldehyde > Ketone > Ester**.