(B)<(C)<(D)<(A)
(A)<(B)<(D)<(C)
(B)<(A)<(D)<(C)
(B)<(C)<(A)<(D)
Correct option is C (B)<(A)<(D)<(C)
In SN1 mechanism the intermediate carbocation formed, more stable the carbocation more is the reactivity.
SN1 Reactivity order Order C > D > A > B.