When \(\mathrm{n}\) -hexane is passed over heated alumina or chromic oxide catalyst under pressure, the product formed is (a) Iso hexane (b) cyclohexane (c) butane and ethane (d) Benzene

We are given that n-hexane is passed over a heated alumina (Al2O3) or chromic oxide (Cr2O3) catalyst under pressure. These catalysts are typically used in dehydrogenation reactions. Dehydrogenation is a process where molecules lose hydrogen atoms and usually form a more unsaturated or cyclic compound.

n-Hexane is a straight-chain alkane with 6 carbon atoms. Its molecular formula is C6H14, and its structure is CH3-CH2-CH2-CH2-CH2-CH3.

We have four possible products: (a) Iso hexane: This would require the shifting of one hydrogen between carbon atoms, but this wouldn't lead to a more unsaturated compound. (b) Cyclohexane: This product would be formed if a carbon-carbon bond is made between the first and the last carbon of n-hexane, and if two hydrogen atoms are lost. This would be a logical outcome of a dehydrogenation reaction. (c) Butane and Ethane: These products would be formed if the n-hexane carbon chain breaks into two smaller alkanes. However, this reaction would not involve a loss of hydrogen atoms, and it would not be consistent with the dehydrogenation process. (d) Benzene: This product would be formed if n-hexane loses six hydrogen atoms and forms three new carbon-carbon double bonds. While possible, this reaction generally requires more severe conditions than that typically used in dehydrogenation reactions involving alumina or chromic oxide catalysts.

Based on our analysis, the product likely formed when n-hexane is passed over alumina or chromic oxide catalyst under pressure is (b) cyclohexane. This product is a reasonable outcome of the dehydrogenation process and is consistent with the reaction conditions.