Which squawk should a pilot use to signify they desire to take on fuel from a tanker?

A squawk code of 70 is specifically designated for airborne refueling operations. When a pilot needs to indicate that they are looking to receive fuel from a tanker, using this squawk code alerts air traffic control and other aircraft in the vicinity to their intentions and operational status.

Using the correct squawk code is essential for maintaining safety and coordination during refueling operations, as it ensures that all parties are aware of the airplane's specific needs and activities. In this context, the other options do not represent the standard communication protocol for indicating a desire to take on fuel from a tanker, making 70 the appropriate choice. Understanding the purpose of these codes is vital for pilots, especially in scenarios involving complex operations like aerial refueling.