Which of the following is a good nucleophile and a strong base?

• A. ${\mathrm{NO}}_3-$ (nitrate ion)
• B. $O_{-}$ (hydroxide ion)
• C. ${\mathrm{Cl}}_{-}$ (chloride ion)
• D. $H_{-}$ (hydride ion)

Answer: (B)

Verified step by step guidance

1. Understand the definitions: A good nucleophile is a species that donates an electron pair to an electrophile, and a strong base is a species that readily accepts a proton (H+). While nucleophilicity and basicity are related, they are not always the same; some ions can be strong bases but poor nucleophiles, and vice versa.
2. Analyze each ion given in the problem: Nitrate ion (NO\_3\^-), hydroxide ion (O\^-), chloride ion (Cl\^-), and hydride ion (H\^-). Consider their charge, electronegativity, and resonance stabilization to assess nucleophilicity and basicity.
3. Nitrate ion (NO\_3\^-) is resonance stabilized, which delocalizes its negative charge, making it a weak base and poor nucleophile.
4. Hydroxide ion (O\^-) has a localized negative charge on oxygen, making it both a strong base and a good nucleophile due to its high electron density and lack of resonance stabilization.
5. Chloride ion (Cl\^-) is a weaker base compared to hydroxide but can be a decent nucleophile; hydride ion (H\^-) is a very strong base but a poor nucleophile in typical organic reactions due to its high reactivity and instability.