Classification of alkanols is based on the

Step 1: Analyze the question The question asks what basis is used to classify alkanols (alcohols) as primary, secondary, or tertiary.

Step 2: Explain the concept Alkanols contain the hydroxyl (-OH) functional group. They are classified by looking at the carbon atom that carries the -OH group (the carbinol carbon) and counting how many other carbon (alkyl) groups are attached to it:

• Primary (1°) alkanol: the carbon with -OH is bonded to one alkyl group (or none, as in methanol). Example: ethanol, CH₃CH₂OH
• Secondary (2°) alkanol: the carbon with -OH is bonded to two alkyl groups. Example: propan-2-ol, (CH₃)₂CHOH
• Tertiary (3°) alkanol: the carbon with -OH is bonded to three alkyl groups. Example: 2-methylpropan-2-ol, (CH₃)₃COH

Step 3: Check each option

• A. Number of carbon atoms in the compound: Wrong. Propan-1-ol and propan-2-ol both have 3 carbons but are different classes.
• B. Molecular mass: Wrong. Isomers have the same molecular mass but can belong to different classes.
• C. Molecular formula: Wrong. Butan-1-ol and 2-methylpropan-2-ol are both C₄H₉OH, yet one is primary and the other tertiary.
• D. Number of alkyl groups bonded to the carbon bearing the hydroxyl group: Correct. This is exactly the criterion for primary, secondary, and tertiary classification.

Step 4: Answer

Exam tip: Remember "look at the carbon holding the OH". Count the carbons attached to it: 1 means primary, 2 means secondary, 3 means tertiary. Isomers (same formula, same mass) can fall into different classes, which is why options A, B and C can never be the basis.