Please help me this question.

so what do you want in this question?
basicity order ?

Basicity is due to electron giving or donating  tendency of an atom and depends on
1)Electronegativity of donor atom
2) Delocalization of lone pair due to resonance.
Now in all these examples  N is the donor atom.
in (b) structure lone pair of nitrogen atoms (sp3) are  delocalized due to resonance and hence creating  formal negative charge on N atom which makes it strongest base.
answer is b
check attached file