(1) LC (L = self inductance, C = capacitance)
The term z(=s/u) has the dimensions of time.
Using the dimensions of

We find that the terms (L/R) and (RC) both have the dimensions of time.

∴ This term also has the dimensions of time.
However, the term [LC] = [T2]
It, therefore, is dimensionally incompatible with the given term, i.e. Z.