waveforms [closed]

Question

Que:-

You are given a free running clock with a duty cycle of 50% and a digital waveform f which changes only at the negative
edge of the clock. Which one of the following circuits (using clocked D flip-flops) will delay the phase of f by 180°?

 

I don't get what is duty cycle of 50% means and  and what is meant by delay the phase by 180?

Comments

It has been observed that you are asking previous year gate questions which are already answered, it is an request please go through  previous section first and find your question if not there then only ask. or

in google type gate overflow and few words of that question you will find what you are looking for