Description of the question:
The question asks for the relay with inherent directional characteristics.

Explanation:
A relay is an electrical device that is used to detect abnormal conditions in electrical circuits and take appropriate actions to protect the system.

Directional characteristic in a relay refers to the ability of the relay to operate only for faults occurring in a specific direction in the electrical circuit. It means that the relay should be able to distinguish between faults occurring in the forward direction and faults occurring in the reverse direction.

Options:
Let's analyze each option to determine which one has inherent directional characteristics:

a) Mho relay:
The mho relay is a distance relay used to protect transmission lines. It measures the impedance seen by the relay and operates when the impedance falls within a certain range. The mho relay has inherent directional characteristics as it operates only for faults occurring in a specific direction.

b) Impedance relay:
The impedance relay is also a distance relay that operates based on the impedance seen by the relay. However, the impedance relay does not have inherent directional characteristics. It operates based on the magnitude of impedance, not the direction.

c) Reactance relay:
The reactance relay is a type of distance relay that measures the reactance seen by the relay. Similar to the impedance relay, the reactance relay does not have inherent directional characteristics.

d) Differential relay:
The differential relay is used to protect transformers, generators, and busbars. It operates based on the difference in current or voltage between two locations. The differential relay does not have inherent directional characteristics.

Conclusion:
Based on the analysis above, the relay with inherent directional characteristics is the mho relay (option A). It is designed to operate only for faults occurring in a specific direction in the electrical circuit.