An absorption peak at 1720 cm in the infrared spectrum typically indicates the presence of a carbonyl group C=O in the compound. The carbonyl group is a common functional group found in various types of organic compounds.To identify the specific type of functional group s present in the compound, we need to consider the possible carbonyl-containing functional groups and their characteristic IR absorption ranges:1. Aldehydes R-CHO : The carbonyl peak for aldehydes usually appears around 1720-1740 cm. Additionally, aldehydes show two distinct peaks for the C-H stretching of the aldehyde group at around 2700-2800 cm and 2800-2900 cm.2. Ketones R-CO-R' : The carbonyl peak for ketones typically appears around 1700-1725 cm.3. Carboxylic acids R-COOH : The carbonyl peak for carboxylic acids usually appears around 1700-1720 cm. Additionally, carboxylic acids show a broad O-H stretching peak around 2500-3300 cm due to the hydrogen bonding.4. Esters R-COO-R' : The carbonyl peak for esters typically appears around 1735-1750 cm.5. Amides R-CONR : The carbonyl peak for amides usually appears around 1630-1690 cm, which is lower than the peak we are considering.Based on the given absorption peak at 1720 cm, the compound could potentially be an aldehyde, ketone, or carboxylic acid. To identify the specific functional group s , we would need to examine other regions of the IR spectrum for additional characteristic peaks e.g., C-H stretching in aldehydes or O-H stretching in carboxylic acids .