Answer
The functional groups in Penicillin G are:
• aromatic
• amide
• cyclic amide
• carboxylic acid
• thioether
Work Step by Step
1. The benzene ring at the left is the aromatic group.
2. The $CO-NH$ group next to the benzene ring is the amide.
3. At the right lower side, the $CO-NH$ is cyclic. It is a cyclic amide.
4. At the upper right side, the structure is of an ether with oxygen replaced by sulphur. This is called a thioether.
5. The lower corner on far right is the carboxylic acid group ($-COOH$)