Which choice represents a pair of resonance structures? note that lone pairs have been omitted for clarity. hints which choice represents a pair of resonance structures? note that lone pairs have been omitted for clarity. o=n−cl and n=o−cl n≡c− and n≡c−h o−s=o and o=s−o h−h and br−br?

Th choice which represent a pair of resonance structures is O - N =O  and O = N - O. 
A resonance pair is another mean of drawing the Lewis structure of a compound. Equivalent Lewis structures are called resonance form. Resonance form is used to spot delocalized electrons; this is done by comparing the electron locations in the two resonance form. If a pair appear in one place in one form and the other pair form and place are different, then the pair is delocalized.