What is the relationship between Gibbs free energy change,enthalpy change,and entropy change?

Which of the following relations is correct?

The standard state Gibbs free energies of formation of $C$ (graphite) and $C$ (diamond) at $T = 298 \ K$ are:
$\Delta_f G^0[C(\text{graphite})] = 0 \ kJ \ mol^{-1}$
$\Delta_f G^0[C(\text{diamond})] = 2.9 \ kJ \ mol^{-1}$
The standard state means that the pressure should be $1 \ bar$,and the substance should be pure at a given temperature. The conversion of graphite [$C$ (graphite)] to diamond [$C$ (diamond)] reduces its volume by $2 \times 10^{-6} \ m^3 \ mol^{-1}$. If $C$ (graphite) is converted to $C$ (diamond) isothermally at $T = 298 \ K$,the pressure at which $C$ (graphite) is in equilibrium with $C$ (diamond) is:
[Useful information: $1 \ J = 1 \ kg \ m^2 \ s^{-2} ; 1 \ Pa = 1 \ kg \ m^{-1} \ s^{-2} ; 1 \ bar = 10^5 \ Pa$ ] (in $bar$)

At a temperature of $25^\circ C$,if $\Delta H < T \Delta S$,then $\Delta G$ = ?

For a given chemical reaction $A \rightarrow B$ at $300 \ K$,the free energy change is $-49.4 \ kJ \ mol^{-1}$ and the enthalpy of reaction is $51.4 \ kJ \ mol^{-1}$. The entropy change of the reaction is $..... \ J \ K^{-1} \ mol^{-1}$.

What is the value of $\Delta G$ for a water system in an environment with a temperature of $100 \ K$?