The mechanism of $S _{ N } 1$ reaction is given as
$R - X \rightarrow R ^{\oplus} X ^{\ominus} \rightarrow R ^{\oplus} \| X ^{\ominus} \stackrel{ Y^\ominus }{\rightarrow} R - Y + X ^{\ominus}$
Ion pair Solvent separated ion pair
A student writes general characteristics based on the given mechanism as:
$(a)$ The reaction is favoured by weak nucleophiles
$(b)$ $R^ \oplus$ would be easily formed if the substituents are bulky
$(c)$ The reaction is accompained by recemization
$(d)$ The reaction is favoured by non-polar solvents.
Which observations are correct $?$