The decreasing order of reactivity of the following compounds towards nucleophilic substitution (S_N2) is :

The major product in the following reaction is :

The mechanism of S_N1 reaction is given as :
A student writes general characteristics based on the given mechanism as :
(a) The reaction is favoured by weak nucleophiles.
(b) R⁺ would be easily formed if the substituents are bulky.
(c) The reaction is accompanied by racemization.
(d) The reaction is favoured by non-polar solvents.

The major product obtained from E₂ - elimination of 3-bromo-2-fluoropentane is