I just recounted and it is definitely 18.

The top half of the consumer unit has all RCBOs supplied from the main switch and six are turned off.

The bottom half of the consumer unit has twelve MCBs all supplied from the RCD, well they would be if the busbar had been installed, but the busbar is missing so all twelve are switched off.

6 + 12 = 18

Fifteen are isolated if it is a TN earthing system, three on the top row by removing the live conductor and terminating them into the earth bar and twelve on the bottom row by removing the live busbar.

The question is clear as mud.

Well I`d go by the two words "switched off" meeself, in the switch is in the off position. If an upstream switch (or RCD) are switched off then the circuits outging are switched off but the MCBs/RCBOs themselves are actually switch on or off as shown. others might disagree

At first sight I would say the entire consumer unit warrants a FI- Further Investigation code, what is the red thing?

I assume it’s supposed to be a SPD, but not as we know it.

Can we all agree it is a dreadful question, and in another country the folk who set it would probably be shot.;-)

Mike.

To put it succinctly, the question simply asks how many devices are switched off and nothing more, no why, no if, nothing. The correct answer to the question they have actualy asked is 11. If they have misworded the question that's their problem. They simply don't understand what they are asking.