Water in a pot of unglazed clay stays cooler than water in a steel pot, on a hot day…

Step 1. (a) A little water seeps through the tiny holes of the clay to the outer surface, and evaporates there. The evaporation takes its latent heat from the pot and from the water inside, so the water stays cool. A steel pot has no holes, so nothing evaporates from its outside.

Step 2. (b) $300\ \text{g} = 0.3\ \text{kg}$, so $Q = mL = 0.3\ \text{kg} \times 2.4 \times 10^{6}\ \text{J/kg} = 7.2 \times 10^{5}\ \text{J}$.