To solve this problem, we will use the formula for osmotic pressure:$\\ \pi = CRT \\$Where:$\\$• $\pi$ is the osmotic pressure.$\\$• $C$ is the concentration in mol L$^{-1}. \\$• $R$ is the universal gas constant.$\\$• $T$ is the temperature in Kelvin.$\\$Given that the plot of $\pi$ vs. $C$ is a straight line with slope $25.73$ L bar mol$^{-1}, \\$we can equate the slope to $RT: \\ RT = 25.73 \\$We are given $R = 0.083$ L bar mol$^{-1}$ K$^{-1}. \\$Substitute $R$ into the equation:$\\ 0.083 \cdot T = 25.73 \\$Solve for $T: \\ T = \frac{25.73}{0.083} \\ T \approx 310$ K$\\$To convert the temperature from Kelvin to Celsius, use the formula:$\\ T_{Celsius} = T_{Kelvin} - 273.15 \\ T_{Celsius} = 310 - 273.15 \\ T_{Celsius} \approx 36.85 \\$Rounding to the nearest whole number, the temperature is approximately $37^\circ$C.$\\$Therefore, the correct option is 3: 37°C.