For a MOD-12 counter, the Flip-Flop has a tpd = 60 ns. The

For a MOD-12 counter, the Flip-Flop has a tpd = 60 ns. The NAND gate has a tpd of 25 ns. The maximum clock frequency is given by—

We know that Maximum frequency is given by

f_max ≤	1
	t_s + n t_Pd

where, n = no. of flip-flop
t_s = propagation delay of gate
t _Pd = propagation delay of flip-flop.
For Mod-12 counter we require 4 flip-flop

f_max ≤	1
	(25 × 10⁻⁹ + 4 × 60 × 10⁻⁹)

or f_max ≤ 3·774 MHz
So, maximum frequency = 3·774 MHz
Hence alternative (C) is the correct answer