To solve this problem, we need to calculate the total energy received by the surface.$\\$Given:$\\$• Average flux (power per unit area) $= 20 \,$W/cm$^2 \\$• Surface area $= 20 \,$cm$^2 \\$• Time duration $= 1 \,$minute$= 60 \,$seconds$\\$First, calculate the total power incident on the surface:$\\$Total power $=$Flux$\times$Area$\\ = 20 \,$W/cm$^2 \times 20 \,$cm$^2 \\ = 400 \,$W$\\$Next, calculate the total energy received by the surface over 1 minute:$\\$Energy $=$Power$\times$Time$\\ = 400 \,$W$\times 60 \,$s$\\ = 24000 \,$J$\\$Therefore, the energy received by the surface during a time span of 1 minute is $24000 \,$J$. \\$This corresponds to Option 2: $24 \times 10^3 \,$J$.$