Consider the following compounds

$1) {\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{NH}}_2$

$2) {\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{NH}-{\mathrm{C}}_6{\mathrm{H}}_5$

3)

$4) {\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{NH}}_2$

Arrange these compounds in decreasing order of their basicity.

Aliphatic amines are more basic nature, when compare to aromatic amines. This is because phenyl group (${\mathrm{C}}_6{\mathrm{H}}_5-$ ) acts as electron withdrawing group. If more number of ${\mathrm{C}}_6{\mathrm{H}}_5-$ groups is attached to ‘N’ atom then basicity gets decrease. Therefore, decreasing order of basicity of the compounds is 4> 1 > 2 > 3  . No. of resonating structures increases, basicity decreases.