Question

Pedro was born in Chile. How would he tell someone his national origin? Yo soy chilena. Son chilenas. Son chilenos. Yo soy chileno.

Answer 1

La respuesta es yo soy Chileno

Answer 2

First, Pedro is a guy (guy = chico). So of course, his nationality would end by "o" not "a", so it's either Son Chilenos, either Yo soy Chileno.
Since Pedro is only one person, So his nationality shouldn't end by "s".
We still got one choice: Yo Soy Chileno. "Yo" can be removed too, and simply say "Soy Chileno".

Hope this Helps! :)