"Es el martes" I think it's wrong. The correct should be "es en martes... isn't it?
No, "en martes" does not work here. That would mean "on a Tuesday".
"On [weekday]" translates to "el [weekday]" in Spanish, since you're talking about a certain day.
No, that doesn't really work, for two reasons.
Spanish doesn't like to do subject-verb inversions in yes-no questions. Such a question usually looks just like a statement, but framed with question marks.
Spanish doesn't like to put two nouns (or noun phrases) right next to each other. If possible, you usually have some buffer in between two nouns, like a preposition or a verb.
the voice recording for this sentence is very poor. there is no indication in the tone of voice that it is a question and not a statement. if I were not looking at the text and could see the question marks I would have translated it as "the concert is on Tuesday" not "is the concert on Tuesday"
If you're tasked to translate a word, you shouldn't abbreviate it. I would even argue that sole weekday abbreviations within sentences are stylistically incorrect.
"Is Tuesday the concert?" is not exactly grammatical in English. English yes-or-no questions follow the pattern Verb-Subject-Objects, but you put the subject "the concert" after the temporal object, "Tuesday".
Why is "es" not placed at the beginning of the sentence as in "es el concierto el martes?"
Spanish yes-or-no questions usually have the same word order as the respective statement, S-V-O. You can also put the verb in the front if you want, but then it's more common to place the subject at the end, V-O-S: "¿Es el martes el concierto?"
Why isn't the name of the day capitalized? Tuesday or martes should be capitalized, right?