The number of unique open-chain structures corresponding to the molecular formula C₃H₅Cl is two.
Step 1. Draw all possible connections of three carbon atoms.
The is only one possibility (See first image below).
Step 2. Put the Cl in all possible unique positions.
There are only two possibilities: on an end carbon or on the middle carbon (see second image below).
Thus, there are only two isomers of C₃H₅Cl.
