(N/A) nucleophile is a species that donates an electron pair to form a chemical bond,while an electrophile is a species that accepts an electron pair.
$1$. $NO_2^+$: Electrophile (contains a positive charge and an electron-deficient nitrogen atom).
$2$. $OH^{-}$: Nucleophile (contains a lone pair of electrons and a negative charge).
$3$. $CH_3NH_2$: Nucleophile (nitrogen atom has a lone pair of electrons).
$4$. $NH_3$: Nucleophile (nitrogen atom has a lone pair of electrons).
$5$. $Br^{+}$: Electrophile (contains a positive charge).
$6$. $CH_3-CO^{-}-CH_3$: Nucleophile (the enolate ion has a negative charge and lone pairs on the oxygen atom).