For an ideal gas, the mean squared velocity \( \langle v^2 \rangle \) is proportional to the temperature \( T \), according to the equation:
\[
\langle v^2 \rangle = \frac{3k}{m} T
\]
where \( k \) is the Boltzmann constant and \( m \) is the mass of the gas molecules.
Analysis:
The equation \( \langle v^2 \rangle = (\frac{3k}{m}) T \) indicates a direct linear relationship between the mean squared velocity and the temperature, with the constant of proportionality being \( \frac{3k}{m} \).
Conclusion:
A graph illustrating a linear relationship between mean squared velocity and temperature should be a straight line passing through the origin with a positive slope. This corresponds to Option (3).