There are three elements X, Y and Z.​

X: It is the element with zero valency.​

Y: Valency of Y is greater than valency of X.​

Z: Valency of Z is greater than X but less than Y.​

Based on information given, identify X, Y and Z respectively

The correct option is A X: He ; Y: N ; Z: Mg​
Valency is zero for noble gases as they have a completely filled valence shell. So X may be Ne or He, not Na. Hence we can eliminate option (C) and (D).
Considering option A neon, magnesium and nitrogen have a valency of 0, 2 and 3 respectively.
Similarly, if we consider option B, helium, nitrogen and magnesium have 0, 3, and 2 as their valency, respectively.
As the valency of Z is less than Y, the correct answer is option (B) not (A).