Uniform Scale in PMMC Type Instrument
The PMMC (Permanent Magnet Moving Coil) type instrument is the only instrument among the given options that has a uniform scale.

Explanation:
The uniform scale refers to a scale in which the divisions or markings are equally spaced. In other words, each division on the scale represents an equal change in the measured quantity.

PMMC Type Instrument:
The PMMC type instrument is a commonly used instrument for measuring DC current or voltage. It consists of a permanent magnet that creates a magnetic field and a moving coil that is suspended in the field. The coil is wound with a large number of turns of fine wire and is connected to a pointer that moves along a calibrated scale.

Working Principle:
When a current flows through the moving coil, it experiences a force due to the interaction between the magnetic field produced by the permanent magnet and the magnetic field produced by the current in the coil. This force causes the coil to rotate, and the pointer attached to the coil moves along the scale.

Uniform Scale in PMMC Type Instrument:
The PMMC type instrument has a uniform scale because the force experienced by the moving coil is directly proportional to the current passing through it. This means that the deflection of the pointer is directly proportional to the current being measured. As a result, the scale can be calibrated in such a way that equal divisions on the scale correspond to equal changes in current.

Other Instrument Types:
a) Moving Iron Type: The moving iron type instrument does not have a uniform scale. The deflection of the pointer in a moving iron instrument is non-linear and depends on the magnitude and direction of the current or voltage being measured.

c) Dynamometer Type: The dynamometer type instrument also does not have a uniform scale. The deflection of the pointer in a dynamometer instrument depends on the product of the currents in both the fixed and moving coils.

d) Electrodynamic Type: The electrodynamic type instrument does not have a uniform scale. The deflection of the pointer in an electrodynamic instrument depends on the interaction between the magnetic field produced by the current and the magnetic field produced by the fixed coil.