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Question:

The increasing order of the pKb of the following compound is:

(C)<(A)<(D)<(B)

(A)<(C)<(D)<(B)

(B)<(D)<(C)<(A)

(B)<(D)<(A)<(C)

Solution:

Order of basicity is B > D > A > C
Hence order of pKb values B < D < A < C
Basicity ∝ +R ∝ 1 -R ∝ +H ∝ 1 -H
As F shows -I effect and NO2 shows -R effect