Compare the relative stability of given carbocations. CH_3- + C...

The stability of alkyl carbocations is determined by the +I effect of alkyl groups and hyperconjugation.

Carbocation I is a tertiary (3^{{}^{\circ}}$) carbocation with 9 \alpha$-hydrogens, providing maximum hyperconjugation and +I effect.

Carbocation II is a secondary (2^{{}^{\circ}}$) carbocation with 6 \alpha$-hydrogens.

Carbocation III is a primary (1^{{}^{\circ}}$) carbocation with 3 \alpha$-hydrogens.

More the number of $\alpha$-hydrogens, more is the hyperconjugation and greater is the stability.

Thus, the relative stability order is I > II > III.

Answer: I > II > III