On the basis of t A. X and Z

B. Y and Z

C. Z and X

D. Z and Y

From the sets of reactions i, ii, iii, it can be observed from i and ii that X is more reactive than Y and hence it displaces Y from its salt.

From reaction iii it can be observed that Z is more reactive than X as it displaces X from its salt.

So the most reactive element is Z and the least reactive is Y.

So correct answer is d [Z and Y].