Which of the following compounds gives a positive iodoform test?

1-phenylethanol

The correct answer is option 4. 1-phenylethanol.

The iodoform test is a chemical test used to detect the presence of methyl ketones or secondary alcohols with a methyl group in the alpha position. The test is positive if a yellow precipitate of iodoform is formed.

The reaction that takes place is as follows:

The first step is the reaction of iodine with sodium hydroxide to form sodium hypoiodite. Sodium hypoiodite is then reacted with the methyl ketone or secondary alcohol to form iodoform and sodium acetate. Iodoform is a pale yellow precipitate, so its formation indicates that the compound being tested contains a methyl ketone or secondary alcohol with a methyl group in the alpha position.

The iodoform test is a very sensitive test, and it can be used to detect even small amounts of methyl ketones or secondary alcohols. It is a useful tool for identifying these compounds in organic samples.

In this question, only 1-phenyl ethanol contains a methyl group at the alpha position w.r.t the secondary alcohol group. So, only 1-phenyl ethanol will show the iodoform test.

So, the correct answer is (4).