Lesser the time-period of the clock, higher the frequency of the clock (i.e) number of clock-cycles per second.
To get the processor with the highest clock-frequency find the processor with the lowest time-period.
P1 : Time period = max ( 1 ns, 2 ns, 2 ns, 1 ns ) = 2 ns
P2 : Time period = max ( 1 ns, 1.5 ns, 1.5 ns, 1.5 ns ) = 1.5 ns
P3 : Time period = max (0.5 ns, 1 ns, 1 ns, 0.6 ns, 1 ns ) = 1 ns
P4 : Time period = max ( 0.5 ns, 0.5 ns, 1 ns, 1 ns, 1.1 ns ) = 1.1 ns
Time-period of P3 < P4 < P2 < P1
So clock frequency of P3 > P4 > P2 > P1.
So P3 has the highest clock-frequency. Option C)