Gibbs free energy ($G$) represents the maximum amount of non-expansion work that can be extracted from a closed system at constant temperature and pressure. It is a thermodynamic potential.
We need to identify which given expression does not correctly represent Gibbs free energy ($G$).
Key thermodynamic relationships are:
Let's examine each option based on the definition $G = H - TS$ and the relationship $H = U + PV$.
Options 2, 3, and 4 represent valid forms of Gibbs free energy ($G$). Option 1, $G = U + TS$, does not represent Gibbs free energy.