Final answer:
A strong peak at 1715 cm^-1 in an infrared spectrum indicates the presence of a carbonyl group, which is common to carboxylic acids, esters, ketones, and aldehydes.
Step-by-step explanation:
A sharp, strong peak observed at 1715 cm-1 on an infrared (IR) spectrum is indicative of the presence of a carbonyl group. Peaks within the 1650-1750 cm-1 range suggest the presence of carbonyl compounds, such as carboxylic acids, esters, ketones, and aldehydes, which tend to absorb in the shorter wavelength end of that range. The strong nature of the peak, in particular, points towards a carbonyl functional group that could belong to one of these types of compounds.