In which one of the following pairs the central atoms exhibit \( sp^2 \) hybridization?
\( \text{BF}_3 \) and \( \text{NO}_2^- \)
\( \text{H}_2\text{O} \) and \( \text{NO}_2 \)
\( \text{NH}_2^- \) and \( \text{H}_2\text{O} \)
\( \text{NH}_2^- \) and \( \text{BF}_3 \)