Answer:
CPU efficiency =$ \frac{\text{useful CPU time}}{ \text{total CPU time}}$
(a) and (b):
The process is executed for time $\textbf T$ and a switch happens when it is blocked.
$\therefore \text {Efficiency} = \dfrac{\textbf T }{\textbf T + \textbf S}$
So, when $\textbf {S = 0}, \text{CPU Efficiency} = \dfrac{\textbf T}{\textbf T} = 100\%$
(c):
$\because \textbf Q<\textbf T$, for each run of $\textbf T$ needs $\dfrac{\textbf T}{\textbf Q}$ process switches, which results in overhead of $\dfrac{\textbf {ST}}{\text Q}$
$\therefore \text {Efficiency }=\dfrac{\textbf T}{\textbf T+\dfrac{\textbf {ST}}{\textbf Q}} = \dfrac{\textbf Q}{\textbf Q + \textbf S}$
So, CPU Efficiency varies from $100\%$ to $50\%$ depending on $\textbf {TQ}$
(d):
Substitute $\textbf Q$ for $\textbf S$ in $\text {(c)}$, and we get $\frac{\textbf Q}{\textbf Q+\textbf Q }= 50%$
So, Efficiency $=50\%$
(e):
$\text{The Efficiency} \to 0\; \text {as} \;\textbf Q \to 0$
So, Efficiency$\approx \textbf0\%$