The order of basicity is II > I > III > IV.

The magnitude of pK_b difference between I and II is more than that between III and IV.

Resonance effect is more in III than in IV.

Steric effect makes compound IV more basic than III.

The acidity of compound I is due to delocalisation in the conjugate base.

The conjugate base of compound IV is aromatic.

Compound II becomes more acidic, when it has a $$-$$NO₂ substituent.

The acidity of compounds follows the order

I > IV > V > II > III.

$${\rm I}$$ and $${\rm I}$$$${\rm I}$$$${\rm I}$$ follow $${S_N}1$$ mechanism

$${\rm I}$$ and $${\rm II}$$ follow $${S_N}2$$ mechanism

Compound $${\rm IV}$$ undergoes inversion of configuration

The order of reactivity for $${\rm I},$$ $${\rm I}{\rm I}{\rm I}$$ and $${\rm IV}$$ is : $${\rm I}V > {\rm I} > {\rm I}{\rm I}{\rm I}$$

$$1$$-chloro-$$4$$-methylbenzene

$$4$$-chlorotoluene

$$4$$-methylchlorobenzene

$$1$$-methyl-$$4$$-chlorobenzene