\({({C_6}{H_5})_3}\dot C\, > \,{({C_6}{H_5})_2}\dot CH\, > \,{(C{H_3})_3}\dot C\, > \,{(C{H_3})_2}\dot CH\)
The stabilisation of first two is due to resonance and last two is due to inductive effect.
$I$ $ -OAc$
$II$ $-OMe$
$III$ $-OSO_2Me$
$IV$ $OSO_2CF_3$
$\mathop {{H_3}C\mathop C\limits^ \ominus {H_2}}\limits_{(i)} \,,$$\mathop {{H_2}C = \mathop C\limits^ \ominus H}\limits_{(ii)} $ અને $\mathop {H - C \equiv \mathop C\limits^ \ominus }\limits_{(iii)} $