Final answer:
The mass spectrum of cyclohexanone is expected to show a molecular ion peak at m/z = 98 due to the combined atomic masses of its carbon, hydrogen, and oxygen atoms summed up in its molecular structure, with the presence of a ketone functional group.
Step-by-step explanation:
To understand why one would expect the mass spectrum of cyclohexanone to show a molecular ion peak at m/z = 98, we need to consider its molecular structure. Cyclohexanone is a six-carbon compound with a ketone functional group. Each carbon atom has a mass of approximately 12 u, the oxygen atom has a mass of 16 u, and the hydrogen atoms have a mass of approximately 1 u each. There are no chlorine atoms or aromatic rings in cyclohexanone, which can be confirmed by looking at its structural formula or IUPAC name. The compound consists of a six-membered ring with 10 hydrogen atoms and one oxygen atom:
- (6 carbons x 12 u) + (10 hydrogens x 1 u) + (1 oxygen x 16 u) = 72 u + 10 u + 16 u = 98 u.
Therefore, the correct answer is b) Presence of a ketone functional group, as the atomic masses of the atoms that make up cyclohexanone add up to a molecular weight of 98 u, which corresponds to the expected peak in the mass spectrum.