The compound shown contains an amine nitrogen and other nitrogens. How many nitrogen atoms in it have a lone pair that is readily available to accept a proton in water (that is, not part of an aromatic sextet)?

Answer: B

The compound shown is histamine. The side-chain primary amine nitrogen has a localised sp3 lone pair, and the imidazole nitrogen without hydrogen has its lone pair in the ring plane, so both are basic. The N-H nitrogen's lone pair is part of the aromatic sextet. Hence 2.

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