x(n)⇌X(z)=∑∞n=03n2+nz2n
In X(z), power of z are even. Therefore, samples in x(n) are available at even instants of time.
By observing all the options. Option (b):
y2(n)⇌Y2(z)=∑∞n=0(5n−n)z−(2n+1)
In Y2(z), powers of z are odd. Therefore, samples in y2(n) are available only at odd instants of time.
Hence, ∑∞n=−∞x(n).y2(n)=0
Thus. x(n) is orthogonal to y2(n).