Football is played in most countries [of/in] the world. Compare of / in.
There are two sentences:

1) Football is played in most countries [of] the world.
2) I'd like to visit every country [in] the world.

Can I use either in/of in each sentences?

Question

Football is played in most countries [of/in] the world. Compare of / in.
There are two sentences:

1) Football is played in most countries [of] the world.
2) I'd like to visit every country [in] the world.

Can I use either in/of in each sentences?

Answer

'in' is correct in both cases, and 'of' is not.
It is possible to say 'of' but really not normal - it's a translation from Spanish or whatever, that many students say.
:)

Answer

Both sentences you wrote are correct. You could use of or in for the football sentence (but of sounds better).  Sentence #2 is better with in, not of.

Não perca a oportunidade de aprender uma língua no conforto da sua casa. Navegue pela nossa seleção de professores de línguas experientes e inscreva-se na sua primeira aula agora mesmo!