Impedence based apex locator is:
(A) Generation 1 (B) Generation 2 (C) Generation 3 (D) Generation 4
(B) Second Generation Apex Locator (Impedance-based Apex Locator) / Low Frequency Apex Locator

Inoue introduced the concept of impedance-based apex locator which measures opposition to flow of alternating current or impedance.
This apex locator indicates the apex when two impedance values approach each other.