The standard reaction Gibbs energy for a chemical reaction at an absolute temperature T is given by G = A - BT, where A…

🧠 Comparing $\Delta G^\circ = A - BT$ with $\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$: $A = \Delta H^\circ$, $B = \Delta S^\circ$ The constant term $A$ equals $\Delta H^\circ$ and the coefficient of $T$ equals $\Delta S^\circ$.

🗺️ Checking each option (a) "Exothermic if $B < 0$": $B = \Delta S^\circ$, so $B < 0$ means $\Delta S^\circ < 0$. That tells us nothing about whether $\Delta H^\circ$ is negative. FALSE ✗

(b) "Endothermic if $A > 0$": $A = \Delta H^\circ$. If $A > 0$, then $\Delta H^\circ > 0$ → endothermic. TRUE ✓

(c) "Endothermic if $A < 0$ and $B > 0$": $A < 0$ → $\Delta H^\circ < 0$ → exothermic, not endothermic. FALSE ✗

(d) "Exothermic if $A > 0$ and $B < 0$": $A > 0$ → $\Delta H^\circ > 0$ → endothermic, not exothermic. FALSE ✗

⚠️ Trap: Students sometimes confuse $A$ and $B$ with $\Delta H$ and $\Delta S$ having the wrong sign. Match term by term: $A$ (constant) = $\Delta H^\circ$; $B$ (coefficient of $T$) = $\Delta S^\circ$.

$\boxed{\text{Answer: (b)}}$