Among the following compounds, which will not undergo oxidation reaction?

2-Methylbutan-2-ol

The correct answer is Option (3) → 2-Methylbutan-2-ol

Oxidation in organic chemistry (especially with common reagents like KMnO₄, K₂Cr₂O₇, or PCC) depends on the presence of hydrogen atoms on the carbon bearing the -OH group (for alcohols) or on the carbonyl carbon (for aldehydes).

Ease of oxidation depends on the type of alcohol:

• Primary alcohol → easily oxidised

• Secondary alcohol → oxidised to ketone

• Tertiary alcohol → resistant to oxidation

• Butanal (CH₃CH₂CH₂CHO): This is an aldehyde with an aldehydic hydrogen (-CHO). It readily undergoes oxidation to butanoic acid.
• Butan-2-ol (CH₃CH(OH)CH₂CH₃): This is a secondary alcohol. Secondary alcohols oxidize to ketones (here, butan-2-one).
• 3-Methylbutan-2-ol (CH₃CH(OH)CH(CH₃)₂): Also a secondary alcohol (the -OH is on a carbon with two alkyl groups and one H). It oxidizes to the corresponding ketone.
• 2-Methylbutan-2-ol ((CH₃)₂C(OH)CH₂CH₃): This is a tertiary alcohol (the carbon bearing -OH is attached to three alkyl groups and no hydrogen). Tertiary alcohols lack a hydrogen on the carbinol carbon and therefore do not undergo oxidation under standard conditions. 

Hence, Option (3)---- 2-Methylbutan-2-ol is the correct answer.