a. I. `3^@` halides , because they form alkenes on eleimination
II. Halides with (`beta` alkyl) group as in neopentyl halides
due to steric hinderance .
III. Vinul and aryl halides [unless activated by o-or po-substituted ` EWG , e.g., (- NO_2)]`, because they do not undergo `ArSN` reaction .
b. I. `Me -NH-Et`
II.
c.
d. i.