First, let us define some of the terms involved.
A carbocation is a species, more specifically, an ion, that contains a positively-charged (hence, cation) carbon atom. On the other hand, a halogenoalkane, is a species that contains one or more halogens (from Group VII) that are derived from alkanes, carbon containing compounds.
Starting from a halogenoalkane, we can get a carbocation through heterolytic fission. The halogenoalkane is split thus releasing a carbocation and a free halide ion. Note that this reaction is reversible - that is, we can form back the starting species, the halogenoalkane. This process is an intermediate step in the so-called Sn1 mechanism, that passes through the carbocation formation step.
Hence, answer is B