The increasing order of stability of the following free radicals is:

Stability of free radicals is increased by:Resonance: Phenyl groups stabilize the radical through delocalization. More phenyl groups mean more stability.Hyperconjugation: Alkyl groups stabilize the radical. $3^{\circ }>2^{\circ }>1^{\circ }$.Resonance stabilization is much stronger than hyperconjugation.$({\text{CH}}_3{)}_2{\text{CH}}^{\bullet }$: $2^{\circ }$ radical.$({\text{CH}}_3{)}_3{\text{C}}^{\bullet }$: $3^{\circ }$ radical.$({\text{C}}_6{\text{H}}_5{)}_2{\text{CH}}^{\bullet }$: Benzylic radical with resonance from two rings.$({\text{C}}_6{\text{H}}_5{)}_3{\text{C}}^{\bullet }$: Benzylic radical with resonance from three rings (triphenylmethyl radical).Order: $({\text{CH}}_3{)}_2{\text{CH}}^{\bullet }<({\text{CH}}_3{)}_3{\text{C}}^{\bullet }<({\text{C}}_6{\text{H}}_5{)}_2{\text{CH}}^{\bullet }<({\text{C}}_6{\text{H}}_5{)}_3{\text{C}}^{\bullet }$.