About Fog: why your normal driving habits no longer apply: which statement is WRONG?
In very dense fog (visibility under 50 metres) three seconds, not two, applies.
As long as your fog lights are on, you don't need to reduce your speed further — others will see you anyway.
Referably do not overtake in dense fog, not even on a motorway.
You follow the right-hand lane as much as possible, so that in an emergency you can use the hard shoulder as a direct escape route.
Explanation
trap: visibility-to-others confused with your own sight. Book p.190-191 - fog lights help others see you, but change nothing about your own reduced sight; you adjust your driving (speed, distance) regardless, once visibility is severely limited