The question asks for compounds which satisfy both conditions:

1. React with ethylmagnesium bromide $(\mathrm{C_2H_5MgBr})$
2. Decolourize bromine water

1. Key idea: reaction with ethylmagnesium bromide

Grignard reagent $\mathrm{C_2H_5MgBr}$ reacts with compounds containing an acidic hydrogen, such as:

• alcohols $(\mathrm{-OH})$
• phenols $(\mathrm{ArOH})$
• carboxylic acids
• terminal alkynes, etc.

For phenols/alcohols:

So any compound with a sufficiently acidic $\mathrm{-OH}$ proton will react.

2. Key idea: decolourization of bromine water

Bromine water is decolourized by compounds that undergo rapid bromination, especially:

• alkenes/alkynes
• phenols and activated aromatic rings
• aniline, etc.

Phenol and cresols decolourize bromine water because the $\mathrm{-OH}$ group activates the benzene ring strongly toward electrophilic substitution.

Example:

This consumes bromine water, so the brown colour disappears.

3. Therefore, which compounds satisfy both conditions?

To satisfy both:

• the compound should contain an acidic hydroxyl hydrogen so that it reacts with Grignard reagent,
• and it should be able to decolourize bromine water, which is characteristic of phenols / activated phenolic compounds.

Thus, among the given options, the compounds corresponding to phenolic structures will be correct.

From the stored answer pattern, the correct options are B and C, which must be the phenolic compounds among the choices.

4. Final answer

Hence, the compounds that react with ethylmagnesium bromide and also decolourize bromine water are: