Arrange the following compounds in the increasing order of polarity...

The polarity of organic compounds depends on the presence of polar bonds and their ability to form hydrogen bonds.

Diethyl ether (A) has C-O bonds but lacks hydrogen bonding capabilities, making it the least polar among the given compounds.

Acetone (C) contains a highly polar C=O double bond, making it more polar than ethers, but it cannot act as a hydrogen bond donor.

Ethanol (B) contains an -OH group, which allows it to form strong intermolecular hydrogen bonds, making it more polar than ketones.

Acetic acid (D) contains both a carbonyl group (C=O) and a hydroxyl group (-OH). This allows for extensive hydrogen bonding (often forming dimers), making it the most polar of the given compounds.

Therefore, the increasing order of polarity is A $<$ C $<$ B $<$ D.

Answer: $\text{A}<\text{C}<\text{B}<\text{D}$