Fill in the blanks:
$(1)$ Each line of the graph of pressure versus temperature (in Kelvin) at a specific molar volume is called ........... .
$(2)$ $A$ gas that strictly follows Boyle's,Charles's,and Avogadro's laws is called ........... .
$(3)$ The ratio of the most probable speed to the average speed is ........... .
$(4)$ The ratio of $U_{rms}$ to $U_{mp}$ is ........... .

(N/A) $(1)$ The graph of pressure versus temperature at constant volume is called an isochore.
$(2)$ $A$ gas that obeys Boyle's law,Charles's law,and Avogadro's law under all conditions of temperature and pressure is called an ideal gas.
$(3)$ The most probable speed $(U_{mp})$ is $\sqrt{2RT/M}$ and the average speed $(U_{av})$ is $\sqrt{8RT/\pi M}$. The ratio $U_{mp} : U_{av} = \sqrt{2} : \sqrt{8/\pi} = 1 : 1.128$.
$(4)$ The root mean square speed $(U_{rms})$ is $\sqrt{3RT/M}$ and the most probable speed $(U_{mp})$ is $\sqrt{2RT/M}$. The ratio $U_{rms} : U_{mp} = \sqrt{3} : \sqrt{2} = 1.224 : 1$.