1.

With Combinational circuits the output(s) depend only on the input(s) but with Sequential circuits the output(s) depend on the state of the flip-flop(s) as well as any input(s) the circuit may have. Therefore Sequential Circuits have a MEMORY and Combinational circuits do not

2.

With Asynchronous logic circuits output(s) can change at any time whenever an input(s) changes but with Synchronous circuits outputs(s) can only change on a transition of the clock pulse.

3.

XY  F
00   1
01   0
10   1
11   1

4.

5.

When D= 0, A=0, B= 1 and C=1
When D= 1, A=0, B= 0 and C= 0

When D=0 the flip-flop TOGGLES (changes state)
When D=1 the flip-flop does NOTHING

5.

YES.... the counter is self-correcting.

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