Right answer is (a) 444 ns
The best explanation: Because the clock pulse of 4-bit transmits the data of 8-bit word in parallel mode and this transmission is done at 2.25 MHz frequency. We know that: f=1/t and we can find the time required for this transmission by the clock pulse.
Therefore, time = (1/2.25) = 0.4444 us = 444.44 ns ~ 444ns.