According to the equation for osmotic pressure, $\pi = CRT$, where $\pi$ is osmotic pressure, $C$ is molarity (concentration in $\text{mol L}^{-1}$), $R$ is the gas constant, and $T$ is temperature in Kelvin .

When a graph is plotted between osmotic pressure ($\pi$) on the y-axis and concentration ($C$) on the x-axis, it gives a straight line with a slope equal to $RT$.

Given slope = $25.73 \text{ L bar mol}^{-1}$ Therefore, $RT = 25.73$ $T = \frac{25.73}{R} = \frac{25.73}{0.083} = 310 \text{ K}$

To convert the temperature to Celsius: $T (^{\circ}\text{C}) = T (\text{K}) - 273 = 310 - 273 = 37^{\circ}\text{C}$.

Hence, the temperature at which the measurement is done is $37^{\circ}\text{C}$.