Explanation

(c)
[image:12_image373.emf] are stabilised hyperconjugation. In [image:12_image374.emf] benzyl group is resonance stabilised. In the triphenyl methyl carbonium ion, the $\pi$-electrons of all the three benzene rings are delocalised with the vacant $p$- orbital of central carbon atom. So, it is resonance stabilised. Therefore, it is most stable of the given carbonium ions.
More the number of resonatic structures more will be the stability.