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NEET levelSingle correct optionDifficulty 1 of 3g2065

Guanidine, $HN = C (NH X_{2}) X_{2}$ , is a very strong organic base (pKaH of guanidinium = 13.6) because

Ait contains three sp $^{3}$ nitrogen atoms with no lone pairs
Bit is a strong acid
Cit has an aromatic ring that withdraws electrons
Dthe guanidinium cation formed on protonation is stabilised by resonance over three equivalent nitrogen atoms

Answer: D

Protonation at the imine nitrogen gives

(H X_{2} N) X_{3} C X^{+}

in which the positive charge is delocalised equally over three N atoms (three equivalent resonance structures). This large stabilisation of the conjugate acid makes guanidine a strong base.

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