Inductance is measured by,

The correct option is Maxwell bridge.

In electrical measurements, AC bridges are used to measure unknown impedances (inductance, capacitance, resistance, and frequency). Let us analyze the purpose of each bridge listed in the options to understand why Maxwell bridge is the correct choice:

1. Maxwell Bridge: This bridge is specifically designed to measure an unknown self-inductance in terms of a known capacitance (Maxwell-Wien bridge) or a known inductance. It is widely used for measuring the inductance of medium-Q coils (Q-factor between 1 and 10).
2. Schering Bridge: This bridge is primarily used for the measurement of unknown capacitance, dissipation factor, and relative permittivity of insulating materials.
3. Kelvin Bridge: This is a DC bridge used for the precise measurement of very low resistances (typically less than 1 ohm).
4. Wien Bridge: This bridge is primarily used to measure audio frequencies. It can also be used to measure capacitance and dielectric loss.

Therefore, the bridge used to measure inductance is the Maxwell bridge.