Explanation
Clock period (CP) = max stage delay + overhead
So CPP1 = Max (1, 2, 2, 1) = 2ns
CPP2 = Max (1, 1.5, 1.5, 1.5) = 1.5 ns
CPP3 = Max (0.5, 1, 0.6, 6, 1) = 1 ns
CPP4 = Max (0.5, 0.5, 1, 1, 1.1) = 1.1ns
As frequency , so least clock period will give the highest peak clock frequency.
So, .