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The least polar compound among the given options is an alkane. This is due to the molecular structure of alkanes, which consist of only carbon and hydrogen atoms connected by single bonds. The difference in electronegativity between carbon and hydrogen is relatively small, leading to nonpolar bonds. Since alkanes are comprised exclusively of these carbon-hydrogen bonds, the overall molecular polarity is minimal.

In contrast, ketones contain a carbonyl functional group (C=O), which is polar due to the significant difference in electronegativity between carbon and oxygen. Alcohols possess an -OH (hydroxyl) group, which also contributes to their polarity, making them capable of forming hydrogen bonds with water. Carboxylic acids, with both a carbonyl and a hydroxyl group, exhibit even greater polarity due to their ability to donate protons and the presence of both polar functional groups.

Overall, the presence of significant polar functional groups in ketones, alcohols, and carboxylic acids contrasts with the nonpolar characteristics of alkanes, establishing alkanes as the least polar option.