A very common mistake made by foreigners speaking Norwegian is that they are mixing up hvis and om . Something that is fully understandable!
Hvis is a conjunction of condition. Om is also a conjunction of condition, but in additionom is used as a subordinated conjunction without expressing any condition, and as a preposition as well.
Expressed in a more general language, this means that to be able to use hvis something has to happen as a result of something else.
“Hvis du spiser opp all fisken, får du en is.” (If you eat up all the fish, you will get an ice cream.)
“Jeg kommer kl 18:00 hvis jeg rekker toget” (I arrive at 6pm if I catch the train.)
If something is not a result of something else, you have to use om .
“Jeg lurer på om han kommer kl 18:00” (I am wondering if he arrives at 6.)
A general rule is that whenever “whether” can replace “if” , om is the correct preposition to use. If you are starting a sentence with om /hvis they are normally interchangeable, but in the moment you use the word in the middle of a sentence you probably have to do with a subordinated conjunction, and the correct word will be om .
Confused? You are not the first one:)
Another simple way to solve this problem is to forget about the word hvis . Om works as three different things (just like a Kinder egg) and can always be used instead of hvis. You may not achieve a perfect academic language that way, but you definitely avoid daily mistakes.