Ambiguous definition of "straight-chain isomers" for C4H9Cl Steps:

• Molecular formula C4H9Cl corresponds to monochlorobutanes with no rings or multiple bonds.
• Carbon skeletons: unbranched (n-butane) gives 2 structural isomers (1-chlorobutane, 2-chlorobutane).
• Branched skeleton (2-methylpropane) gives 2 more (1-chloro-2-methylpropane, 2-chloro-2-methylpropane).
• Total structural isomers: 4; "straight-chain" typically means only unbranched (2), but unclear if it excludes branched here. Not enough information.

Final answer: Not enough information.