The correct IUPAC name of ${\mathrm{C}}_2{\mathrm{H}}_5-\underset{\underset{{\mathrm{CH}}_3}{|}}{\mathrm{N}}-{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3$ is

N,N – diethyl butylamine

N-Ethyl – N – methyl butylamine

N- Ethyl – N – methyl butanamine

N- Ethyl – N – methyl Propan -1- amine