Question

Sol. Key concept: A more stable radical generally corresponds to a weaker bond broken homolytically.

Removal of H_b forms a diphenylmethyl radical, delocalised over two phenyl rings. Removal of H_a forms a benzyl-type radical, delocalised over one phenyl ring. Removal of the aryl hydrogen H_c produces a much less favourable aryl radical.

The radical stability order is b > a > c, so the C–H bond-strength order is reversed: C–H_c > C–H_a > C–H_b. This is the order printed in option (d).

Correction / clarification: The stem requests an increasing order, while all options use >. The increasing order is C–H_b < C–H_a < C–H_c; it is equivalent to the decreasing order in (d).