Which of the following is an electrophilic reagent?

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 $DMSO$

Which of the following species acts as an electrophile?

The cyanide ion $(CN^-)$ is:

What are ambident nucleophiles? Explain with detailed examples.

The number of nucleophiles in the following list is $CH_3NH_2$,$CH_3CHO$,$C_2H_4$,$CH_3SH$.