Final answer:
Gliders not in contact with ATC should squawk code '1202', which helps ATC differentiate them from other VFR traffic. The provided options A) 7500, B) 7600, C) 7700, and D) 7800 are emergency codes, and none are correct for this situation.
Step-by-step explanation:
The subject of this question is concerned with aviation, specifically transponder codes used by gliders when they are not in contact with Air Traffic Control (ATC). When a glider is not in contact with ATC, the pilot should squawk a particular transponder code to be identified correctly by ATC radar. The correct code for the pilot to squawk, in lieu of the normal VFR (Visual Flight Rules) code of 1200, is '1202'. This code is used for gliders to help ATC differentiate them from other VFR traffic. It should be noted that none of the options provided (A) 7500, (B) 7600, (C) 7700, or (D) 7800 are correct. These codes are emergency codes: 7500 indicates hijacking, 7600 indicates radio failure, and 7700 indicates a general emergency. There is no standard 7800 code.