Q1: What decimal value is required to produce an output at "X" ?

ANS:D - 5

JK flip-flop operation.

Here, notice that both the inputs i.e., J and K are tied together and given. Therefore the only possible input conditions for JK flipflop are (j=0& k=0) or (j =1 and k=1).

Now we are in J=1, K=1 condition, which means the present output Q should be the toggled version of previous state output.

The previous state output will obviously be for j= 0 and k=0 input condition. The output, in this case, will be 0 only (retains the previous state for j=0 and k=0 condition) - check truth table for jk flip flop.

This is how the first flip flop's output becomes 1 (toggle of previous state output 5, 0).

Now consider second flip-flop, the same condition repeats but the output is taken from Qbar pin of the flipflop. Therefore second flipflop's output is 0.

The third one follows similar explanation as given for first flip-flop. Output turns out to be 1 again.