Would someone please explain the difference between "meu pé" and "o meu pé?" The second option is counted as a wrong solution, though I'm not sure if it's a technical problem or actually incorrect.
both are correct. since you use the possessive as an adjective, you can choose wheter or not use the definite article. but, if you use them as pronouns, you cant leave the definite article out.
Yes, you can say either. Though it's common with body parts to leave out the possessive and just say "O pé".