Which of the following statements is not correct?

The stability of carbocations follows the order: ${\mathrm{CH}}_3^{+}>{\mathrm{CH}}_3{\mathrm{CH}}_2^{+}>{\left({\mathrm{CH}}_3\right)}_2{\mathrm{CH}}^{+}>{\left({\mathrm{CH}}_3\right)}_3{\mathrm{C}}^{+}$

Nucleophilic substitution reaction involving ${\mathrm{S}}_{\mathrm{N}}1$ mechanism may involve the inversion of configuration of carbon atom.

Nucleophilic substituion reaction involving ${\mathrm{S}}_{\mathrm{N}}2$ mechanism is always associated with the inversion of configuration of carbon atom.

The ${\left({\mathrm{CH}}_3\right)}_3\dot{\mathrm{C}}$ is more stable than ${\left({\mathrm{CH}}_3\right)}_2\dot{\mathrm{C}}\mathrm{H}$