Refer to figure.
The image shows a transponder, not an ADF, which would be used to navigate with reference to an NDB ground station.

A transponder can be of 3 main types:

• Mode-A: These transponders are the simplest of all types, they transmit a 4 digit code, with each digit being a number from 0-7 (4096 combinations). They transmit this code after a suitable interrogation signal from a ground system, and the ground controller can see location and transponder code.
• Mode-C: The same as Mode-A, but with the addition of a pressure altitude output (to the nearest 100 ft), which can be seen by the controller on the ground. Any Mode-C transponder can also perform Mode-A operations if the pilot chooses.
• Mode-S: A much more capable type of transponder, transmitting not just transponder code and altitude (more accurate than Mode-C), but also the hard coded ICAO address of that aircraft. It can also selectively call certain aircraft, or all aircraft, to improve capability with high traffic densities, and is compatible with both Mode-A and Mode-C systems, as well as ADS-B and enhance mode-S surveillance, allowing for a multitude of aircraft parameters to be broadcast.

The figure in the question shows a transponder which clearly outputs pressure altitude (in 100 ft increments - though that is not enough alone to be sure it is Mode-C). We can, however, see that there are no indications of aircraft address, nothing to do with ADS-B and no included TCAS system (which is often included in a mode-S transponder), so there is no evidence it is a Mode-S transponder.

This is, in the examiner's eyes, a mode-C transponder. To our knowledge, this exact type of transponder can come in two types, Mode-A/C and a basic Mode-S (no enhanced functionality), however, from purely the information in the figure, we have to say it is Mode-C, as everything points toward that.

The controls on the right are not transponder controls, those are extra functions such as flight timers, etc.