Which of the following types of alkanols undergo oxidation to produce alkanoic acids. I. Primary alkanols II. Secondary alkanols III. Tertiary alkanols

Analyze the question: We need to know which classes of alcohols (alkanols) can be oxidised to give alkanoic (carboxylic) acids.

Concept: The oxidation of an alcohol depends on how many hydrogen atoms are attached to the carbon bearing the –OH group (the carbinol carbon).

• Primary alkanols (RCH₂OH) have 2 H atoms on that carbon. They oxidise first to an alkanal (aldehyde), then further to an alkanoic acid when an oxidising agent such as acidified K₂Cr₂O₇ or KMnO₄ is used. RCH₂OH → RCHO → RCOOH
• Secondary alkanols (R₂CHOH) have 1 H atom. They oxidise to alkanones (ketones) only. Ketones resist further oxidation without breaking C–C bonds, so no alkanoic acid with the same number of carbons forms. R₂CHOH → R₂C=O
• Tertiary alkanols (R₃COH) have no H on the carbinol carbon. They resist oxidation under normal conditions.

Solution:

• I. Primary alkanols → alkanoic acids ✔
• II. Secondary alkanols → alkanones ✘
• III. Tertiary alkanols → no oxidation ✘

Only primary alkanols produce alkanoic acids, which matches option D.

Tip: Remember "Primary → Aldehyde → Acid; Secondary → Ketone (stop); Tertiary → No reaction." Count the hydrogens on the carbon carrying the –OH: 2 H leads to an acid, 1 H gives a ketone, and 0 H means no reaction.