Hey ahundadavid07, good to see you again. Here's the solution for Q2.b.ii: Step 1: Calculate the ideal efficiency of the fuel cell. The ideal efficiency ($\eta$) of a fuel cell is given by the ratio of the Gibbs free energy change ($\Delta G$) to the enthalpy change ($\Delta H$). $$ \eta = \frac{\Delta G}{\Delta H} $$ Given: $\Delta G = -237 \text{ kJ/mol}$ $\Delta H = -286 \text{ kJ/mol}$ Substitute the values: $$ \eta = \frac{-237 \text{ kJ/mol}}{-286 \text{ kJ/mol}} $$ $$ \eta \approx 0.82867 $$ Convert to percentage: $$ \eta \approx 0.82867 \times 100\% $$ $$ \eta \approx 82.87\% $$ The ideal efficiency of the fuel cell is $\boxed{\text{82.87%}}$. Step 2: Give two reasons why hydrogen is difficult to store. • Hydrogen has a very low volumetric energy density, meaning a large volume is required to store a significant amount of energy, even when compressed or liquefied. This necessitates high-pressure tanks or cryogenic temperatures, which are energy-intensive and costly. • Hydrogen is highly flammable and explosive when mixed with air, posing significant safety challenges for storage and transportation. Send me the next one 📸