I've read on one of these sentences that "hvis" and "om" (possibly also some other words) are interchangeable when used as "if". I just wanted to know if one is used more often than the other in general or does it vary from person to person or maybe there is a particular time to use each of them? Takk på forhånd ^^
I think 'om' is most common in general, but there are some contexts where 'hvis/viss' would be preferred. For instance if you're making a condition:
if-else = hvis/viss-ellers
If they have milk, buy eggs, or else I'm not going to bake this cake.
Viss/Hvis de har melk, kjøp egg, ellers kommer jeg ikke til å lage denne kaka.
(Notice that the adverb 'ikke' precedes the verb in such sentences)
if-then = hvis/viss-så
If you want to, (then) you can come along.
Viss/Hvis du vil, (så) kan du få bli med.