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

The current in a triode at anode potential $100 \, V$ and grid potential $-1.2 \, V$ is $7.5 \, mA$. If the grid potential is changed to $-2.2 \, V$, the current becomes $5.5 \, mA$. The value of transconductance $(g_m)$ will be .... $mili \, mho$.

The value of the amplification factor from the following graph is:

In the figure,four plate characteristics of a triode at different grid voltages are shown. The difference between successive grid voltages is $1 \ V$. Which curve will have the maximum grid voltage and what is its value?

In the mutual characteristic curve of a triode,which point represents the cut-off voltage?

If the amplification factor of a triode $(\mu)$ is $22$ and its plate resistance is $6600 \, \Omega$,then the mutual conductance of this valve in mho is: