Recall the condition for iodoform test

A compound gives iodoform reaction if it contains either:

• a methyl ketone group: $\ce{R-CO-CH3}$, or
• an alcohol of type $\ce{CH3-CH(OH)-R}$, because it gets oxidized to a methyl ketone.

Also, ethanol gives the test because it is oxidized to ethanal, which behaves positively.

Check each molecule one by one

(i) Ethanol: $\ce{CH3CH2OH}$

Ethanol is oxidized to ethanal $\ce{CH3CHO}$, which gives iodoform test.

$\Rightarrow$ Gives iodoform reaction

(ii) Isopropyl alcohol: $\ce{CH3-CHOH-CH3}$

This is a secondary alcohol of type $\ce{CH3-CH(OH)-R}$. On oxidation, it forms acetone $\ce{CH3COCH3}$.

$\Rightarrow$ Gives iodoform reaction

(iii) Bromoacetone: $\ce{CH3COCH2Br}$

It contains the methyl ketone group $\ce{CH3CO-}$.

$\Rightarrow$ Gives iodoform reaction

(iv) 2-Butanol: $\ce{CH3-CH(OH)-CH2CH3}$

This is of type $\ce{CH3-CH(OH)-R}$. On oxidation, it gives 2-butanone $\ce{CH3COCH2CH3}$, a methyl ketone.

$\Rightarrow$ Gives iodoform reaction

(v) 2-Butanone: $\ce{CH3COCH2CH3}$

This is a methyl ketone.

$\Rightarrow$ Gives iodoform reaction

(vi) Butanal: $\ce{CH3CH2CH2CHO}$

This is not ethanal and does not contain $\ce{CH3CO-}$.

$\Rightarrow$ Does not give iodoform reaction

(vii) 2-Pentanone: $\ce{CH3COCH2CH2CH3}$

This is a methyl ketone.

$\Rightarrow$ Gives iodoform reaction

(viii) 3-Pentanone: $\ce{CH3CH2COCH2CH3}$

This is not a methyl ketone because carbonyl carbon is attached to $\ce{CH2CH3}$ on both sides.

$\Rightarrow$ Does not give iodoform reaction

(ix) Pentanal: $\ce{CH3CH2CH2CH2CHO}$

Aldehyde other than ethanal.

$\Rightarrow$ Does not give iodoform reaction

(x) 3-Pentanol: $\ce{CH3CH2CH(OH)CH2CH3}$

On oxidation it gives 3-pentanone $\ce{CH3CH2COCH2CH3}$, which is not a methyl ketone.

$\Rightarrow$ Does not give iodoform reaction

Count molecules which do NOT give iodoform reaction

The compounds which cannot give iodoform reaction are:

• Butanal
• 3-Pentanone
• Pentanal
• 3-Pentanol

Total $= 4$

Match with option

$\boxed{4}$ corresponds to Option A.