Correct or incorrect 1) que harremos manana?
2) yo poderia salir manana.
3) ellas nunca estuvieron tan cansadas.
4) los animales son protegen por leyes.
5) una guitarra tiene tantas cuerdas de un guitarron.
6) no quiero tu archivo, quiero el mio.
7) quieren ir a esa fiesta?
8) tengo que esperar por el autobus.

explain why for each one.

I do not see any accent symbol in any word, so i guess you did not put them, and i will not consider that a missing accent symbol is an incorrect option because maybe in the original question they are there.

1) Incorrect, there two misspelled words, Haremos goes with only an r and Mañana goes with an "Ñ" instead of an "N" in the first place.

2) The second word is misspelled, it is "Podria"

3) This is correct.

4) This has  

no coherence, "protegen" is wrong here, the actual word must be "protegidos"

5) This has no coherence, this should be written as "una guitarra tiene tantas cuerdas COMO un guitarron" (a guitarron is like a larger guitar that has the place of the "bass" in the band)

6) This is correctly written

7) This is correctly written

8) This is incorrect, it should say "Tengo que esperar Al autobus" instead de "por el"