Below is a list of five tripeptides identified by their single letter codes. which tripeptide is negatively charged at physiological ph?

The list of the given tripeptides are as follows: FNC, RGK, VIL, MDE and SYT. 
The nature of an amino acid depend on the types of side chain which it possesses. In order to determine the type of charge that a protein caries, one has to know the amino acid that are linked together in the protein and their sequences.
In the question given above, the correct option is MDE.
The one letter symbols for proteins are used to represent the tripeptides given in the question and MDE stands for Methionine - Aspartate - Glutamate. Methionine  has a non polar side chain while both aspartate and glutamate have acidic side chains. The acidic side chains will confer a negative charge on the tripeptide MDE at physiological pH.