GIVEN : assuming that each process has its own i/o resource.
(GANTT CHART FOR I/O OF PROCESSOR $\mathbf{P_1, P_2 ,P_3}$)
EXPLANATION :
Here, $P_2$ has the least priority and $P_1$ has the highest.
$P_1$ enters CPU at $0$ and utilizes it for $1$ time unit. Then it performs i/o for $5$ time units.
Then $P_2$ enters at time unit $2$ and requires $3$ time units of CPU. But $P_3$ whose priority is greater than $P_2$ arrives at time unit $3$.
So, $P_2$ IS PREEMPTED (only $1$ unit of $P_2$ is done out of $3$ units. Therefore $2$ units of $P_2$ are left out) AND $P_3$ ACQUIRES THE CPU. Once $P_3$ finishes, $P_2$ enters the CPU to complete its pending $2$ units job at time unit $5$. AGAIN BY THEN $P_1$ finishes its i/o and arrives with a higher priority. Therefore of $2$ units $P_2$ performs only one unit and the CPU is given to $P_1$.Then when $P_1$ is performing in CPU, $P_3$ completes its i/o and arrives with a higher priority.Thus the CPU is given to $P_3$ ($1$ UNIT IS USED). $\mathbf{P_3}$ FINISHES AT TIME UNIT 9. NOW PRIORITY OF $P_1$ IS MORE THAN $P_2$, SO, CPU IS USED BY $P_1$. $\mathbf{P_1}$ FINISHES BY TIME UNIT 10. THEN CPU IS ALLOCATED FOR PROCESS $P_2$. $\mathbf{P_2}$ PERFORMS REST OF ITS WORK AND FINISHES AT TIME UNIT 15.
THEREFORE,
FINISH TIME OF $P_1,P_2,P_3$ ARE $10,15$ AND $9$ RESPECTIVELY. 😊
Correct Answer: $B$