See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Oxidation in organic chemistry is defined as a process that involves an increase in the oxidation state of carbon, which typically corresponds to: loss of hydrogen, gain of oxygen, or gain of a more electronegative element (relative to hydrogen). We analyze each reaction by tracking the oxidation state of the relevant carbon atoms. Reaction (1): n-Butane (CH3CH2CH2CH3) --> Butanone (CH3COCH2CH3) In butane, the central carbons are bonded only to C and H. In butanone, the carbonyl carbon (C=O) has replaced two C-H bonds with a C=O bond. The carbon goes from a lower oxidation state to a higher one (oxygen is more electronegative than H). This is an oxidation of the reactant. ✓ Reaction (2): Acetone (CH3COCH3) --> Methyl acetate (CH3COOCH3) In acetone, the carbonyl carbon has oxidation state: bonded to two CH3 groups and one =O. In methyl acetate, the carbonyl carbon is bonded to one CH3, one =O, and one -OCH3. The carbon has gained an additional bond to oxygen (a more electronegative atom). The oxidation state of the carbonyl carbon increases. This is an oxidation of the reactant. ✓ Reaction (3): Benzene --> Cyclohexane Benzene (C6H6) is converted to cyclohexane (C6H12). The carbons in benzene each bear one H, while in cyclohexane each carbon bears two H atoms. Carbon has gained hydrogen (reduction means gaining H or losing O). This represents a REDUCTION of the reactant, not oxidation. ✗ Reaction (4): CH2=CH2 --> CH3-CH2-Cl Ethylene gains HCl (addition reaction). The carbon goes from sp2 (double bond) to sp3 with one Cl. While Cl is electronegative, this is formally an addition reaction. Checking oxidation states: each carbon in ethylene is -1 (approximately); in chloroethane, the CH3 carbon is -3 and the CH2Cl carbon is 0. One carbon is oxidized and one is reduced — this is neither a net oxidation nor purely an oxidation of the overall reactant. ✗ Therefore, only reactions (1) and (2) show oxidation of the reactant. Why other options fail: - Option (a) says only reaction 1: misses reaction 2 which is also oxidation. - Option (c) says 1, 2, 3: reaction 3 is a reduction (benzene to cyclohexane adds hydrogen). - Option (d) says all: reactions 3 and 4 are not oxidations. Therefore, the correct answer is B.