Q17) Answer : A
Its A because the allocation : (4,4) & (2,0) for agents 1 and 2 is a point of competitive equilibrium right?
Or is there any other reason (since endowments are not given so I'm not able to think of any other reason.)?

Answer seems to be B.
First find the set of pareto-optimal(PO) allocations.
Then take any value of px with py=1 and solve optimization prob. for both agents.
Check if your optimal soln. clears market. If yes then prices are competitive.

But how would I do that without their respective endowments? I mean I'd need their incomes to do that right?
By the way the answer is given as A in the key that I'm following.