Concept used: Nucleophilicity is the tendency of a species to donate an electron pair to an electron-deficient center.

General trend: For species with the same attacking atom, nucleophilicity usually increases with:

• greater negative charge,
• lower electronegativity,
• higher availability of lone pair.

Check option A: $\mathrm{F^- > OH^-}$

• Compare $\mathrm{F^-}$ and $\mathrm{OH^-}$.
• The attacking atoms are F and O.
• Oxygen is less electronegative than fluorine, so the lone pair on $\mathrm{OH^-}$ is generally more available for donation than on $\mathrm{F^-}$.
• Thus, $\mathrm{OH^-}$ is generally more nucleophilic than $\mathrm{F^-}$.
• So option A is incorrect.

Check option D: $\mathrm{NH_2^- > NH_3}$

• Both have nitrogen as the donor atom.
• $\mathrm{NH_2^-}$ carries a negative charge, while $\mathrm{NH_3}$ is neutral.
• The anion has greater electron density and donates its lone pair more readily.
• Therefore, $\mathrm{NH_2^- > NH_3}$
• So option D is correct.

Since among the visible options, D gives a correct nucleophilicity order, the answer is: $\boxed{\mathrm{NH_2^- > NH_3}}$