The capacity of parallel plate condenser is dependent on the

The correct option is "The separation between the plates".

To understand why this is the correct answer, let us look at the formula for the capacitance (capacity) of a parallel plate condenser (capacitor):

$$C=\frac{{\epsilon }_0{\epsilon }_{r}A}{d}$$

Where:
- _C represents the capacitance of the parallel plate condenser.
- _ε0 is the permittivity of free space (a constant).
- _εr is the relative permittivity (dielectric constant) of the medium between the plates.
- _A is the overlapping area of the plates.
- _d is the separation distance between the plates.

From this formula, we can clearly see that the capacitance _C is:
1. Directly proportional to the area of the plates (_A).
2. Directly proportional to the permittivity of the dielectric medium (_εr).
3. Inversely proportional to the distance of separation between the plates (_d).

Therefore, the capacity depends directly on the separation between the plates. It does not depend on the thickness of the plates, the type of metal used for construction, or the potential applied across the plates.