The correct option is A −101376
(a−2b)12=[a+(−2b)]12
General term Tr+1=C(12,r)a12−r(−2b)r
Putting 12−r=5 or 12−5=r⇒r=7
T7+1=C(12,7)a12−7(−2b)7=C(12,7)a5(−2b)7=C(12,7)(−2)7a5b7
Hence required coefficient is C(12,7)(−2)7=!2!7!5!⋅27=−12×11×10×9×8×7!7!×5×4×3×2×1×27
=−11×9×27=−99×128=−101376