The stability of a carbonium ion (carbocation) formed after the heterolytic cleavage (ionization) of a C-Cl bond depends on how well the positive charge is dispersed. Factors that stabilize carbocations include resonance (e.g., benzylic or allylic cations, or stabilization by adjacent atoms with lone pairs via $+R$ effect), hyperconjugation (a greater number of $\alpha$-hydrogens makes tertiary $>$ secondary $>$ primary), and positive inductive effects ($+I$). Because the structural formulas for the options are missing from the provided text, the specific compounds cannot be evaluated to determine which forms the most stable carbocation.