Is it written “se” or “sé”?

Both forms are correct.Se, without the accent, it is a hypothetical conjunction which serves to introduce a hypothesis or a condition.

Se avessi tempo, andrei a fare una passeggiata al mare.

Se fossi ricco, comprerei uno yacht.

Se tu mi dessi attenzione, ti spiegherei cosa è successo.

,with the accent, it is instead the third person singular reflexive pronoun.

Marco pensa solo a stesso.

 Chi fa da fa per tre.

Le critiche di questo genere può tenersele per .

As it can be seen from the first example, in the locution sé stesso, “se” requires the accent as it performs the function of a reflexive pronoun.The two words are homonymous that is  they have the same form and are pronounced the same way but have a different meaning. In Italian, the accent is used to distinguish the meaning of two homonymous words.

“Se” or “sé”? Indicate whether the sentences are true or false.