Which of the following behaves as both a nucleophile and an electrophile?

In each of the following groups,which is the strongest (best) nucleophile?
$(I)$ $(1)$ $H_3C-O^-$,$(2)$ $CH_3CH_2O^-$,$(3)$ $H_3C-S^-$ in $CH_3OH$
$(II)$ $(1)$ $OH^-$,$(2)$ $H_2O$,$(3)$ $NH_2^-$ in $DMF$
$(III)$ $(1)$ $(CH_3)_2CH-O^-$,$(2)$ $O^-$,$(3)$ $CH_3O^-$ in $DMSO$

Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles:
$(a) \ CH_{3}COOH + \mathbf{HO^{-}} \to CH_{3}COO^{-} + H_{2}O$
$(b) \ CH_{3}COCH_{3} + \mathbf{CN^{-}} \to (CH_{3})_{2}C(CN)OH$
$(c) \ C_{6}H_{6} + \mathbf{CH_{3}C^{+}=O} \to C_{6}H_{5}COCH_{3} + H^{+}$

Which one of the following characteristics belongs to an electrophile?

Which of the following is a nucleophile?

Which of the following statements is true?