Pyridine is basic in nature due to the presence of free lone pair. Its basicity gets affected by the presence of different substituents attached to it. The electron withdrawing group decreases the basicity of pyridine, whereas electron releasing groups increases its basicity.
Substituents like N(Me)2 and CH3 are electron releasing but N(Me)2 is more activating group than CH3.
So
basicity would be maximum while Cl is an electron withdrawing group, so
is basicity would be least.
The increasing order of basicity of compounds given in options will be