When are you allowed to use fog headlamps also during the day?

Fog headlamps may be used in daytime when visibility is significantly reduced by fog, falling snow, or heavy rain. The idea is that these lights are designed to illuminate the road close in front of your vehicle while producing less glare from water droplets than normal dipped headlights, so you can see the road edge and markings better in bad weather.

Your selections 1 and 2 are correct because both situations can reduce visibility enough to justify fog lights. In Germany, fog headlamps are not “fair-weather extras”; you should only switch them on when weather conditions really limit visibility. If the weather improves, turn them off again so you don’t unnecessarily dazzle or annoy other road users.

Answer 3 is not a reason to use fog headlamps. Ice on the windscreen is a vehicle condition, not a visibility situation you’re allowed to “solve” with lighting. The correct rule of thumb is: if your windscreen is iced up, you must clear it properly before driving; lights never replace a clear view.