The voltage gain of a triode depends upon

What is the effect of $SCR$ (Space Charge Region) in a vacuum tube?

On applying a potential of $-1 \ V$ at the grid of a triode,the following relation between plate voltage $V_p$ $(V)$ and plate current $I_p$ (in $mA$) is found:
$I_p = 0.125 V_p - 7.5$
If on applying $-3 \ V$ potential at the grid and $300 \ V$ potential at the plate,the plate current is found to be $5 \ mA$,then the amplification factor of the triode is:

Before the saturation state of a diode,at plate voltages of $400 \, V$ and $200 \, V$,the currents are $i_1$ and $i_2$ respectively. The ratio $i_1/i_2$ will be:

The mutual characteristic curves of a triode are as shown in the figure. The cut-off voltage for the triode is.....$V$.

The relation between dynamic plate resistance $(r_p)$ of a vacuum diode and plate current $(I_p)$ in the space charge limited region is: