The reaction,

is fastest when X is `:`

Rate of the reaction : is fastest when Z is :

Rate of the reaction is fastest when Z is -

SN^1 reaction is fastest in

Rate of the reaction. is fastest when Z is

S_(N^1) reaction is fastest in

Rate of the reaction of fastest when 'Z' is R-overset(O)overset(||)(C)-Z+Nu^(-) rarr R - overset(O)overset(||)(C)-Nu + Z^(-)