Which of the following reactions is S_N¹ type?

(i)

(ii)

S_N¹ reaction type proceeds through formation of 3° carbocation which has planar geometry. Now this intermediate is attacked from both sides of the plane so the resultant product follows both retention and inversion of stoichiometry. Reaction (i) shows inversion of stoichiometry and reaction (ii) shows retention. Thus, both of the above products are possible by S_N¹ reaction type.