To solve this problem, we need to identify the compound 'X' based on the given reactions and properties.$\newline$The molecular formula of 'X' is $C_5H_{10}O. \newline$Let's analyze the clues provided:$\newline$• 'X' yields phenyl hydrazone: This indicates that 'X' is a carbonyl compound (either an aldehyde or a ketone).$\newline$• 'X' gives a negative response to the iodoform test: This means 'X' does not have a methyl ketone group $(CH_3CO-). \newline$• 'X' gives a negative response to Tollen's test: This indicates 'X' is not an aldehyde.$\newline$• 'X' produces n-pentane on reduction: This suggests that 'X' is a ketone, as reduction of a ketone will yield an alkane.$\newline$Based on these clues, 'X' must be a ketone that does not have a methyl group adjacent to the carbonyl group.$\newline$Let's analyze the options:$\newline$Option 1: 2-pentanone$\newline$• 2-pentanone has the structure CH_3CH_2COCH_2CH_3.$\newline$• It has a methyl group adjacent to the carbonyl, so it would give a positive iodoform test.$\newline$• Therefore, it is not 'X'.$\newline$Option 2: 3-pentanone$\newline$• 3-pentanone has the structure CH_3CH_2CH_2COCH_3.$\newline$• It does not have a methyl group adjacent to the carbonyl, so it gives a negative iodoform test.$\newline$• It is a ketone, so it gives a negative Tollen's test.$\newline$• On reduction, it will yield n-pentane.$\newline$• Therefore, 3-pentanone is a suitable candidate for 'X'.$\newline$Option 3: n-amyl alcohol$\newline$• n-amyl alcohol is an alcohol, not a carbonyl compound, so it cannot form phenyl hydrazone.$\newline$• Therefore, it is not 'X'.$\newline$Option 4: pentanal$\newline$• Pentanal is an aldehyde, which would give a positive Tollen's test.$\newline$• Therefore, it is not 'X'.$\newline$Based on the analysis, the correct option is Option 2: 3-pentanone.