Rate of  $S_{N}1$ reaction is increased based on by following factors because:

good leaving groups (more stable anions) lower the energy of the transition state leading to carbocation formation thus increasing the reaction rate

a non basic nucleophile (like $H_{2}O$) will prevent a competitive E₂ reaction

polar solvents stabilize the carbocation intermediate by solvation, thereby increasing the reaction rate

none of the above