How does mode S identify each aircraft?

A)
RCS
B)
Unique code for each transponder
C)
Lapsed time
D)
Directly talking to the pilot

Correct Answer :   Unique code for each transponder


Explanation : Unlike the ATCRBS where a squawk code is dialed into the transponder, a mode S transponder has a unique identity permanently assigned to it. The mode S radar system can have more than 16 million different identities, enough for each airplane in the world to have a unique identity.