Reaction of cyclohexanone with dimethylamine in the presence of catalytic amount of an acid forms a compound if water during the reaction is continuously removed. The compound formed is generally known as

The decreasing order of nucleophilicity among the nucleophiles

The reaction



is fastest when $$X$$ is

A schematic plot of $$ln$$ $${K_{eq}}$$ versus inverse of temperature for a reaction is shown below


The reaction must be