If "alguno" means "some":
* Ninguno: This means "none" and is the most direct opposite of "some".
* Nada: This means "nothing" and can also be used as the antonym for "some" in certain contexts.
If "alguno" means "any":
* Ningún: This means "no" or "not any" and is the direct opposite of "any".
* Ninguno: This means "none" and can also be used as the antonym for "any" in certain contexts.
If "alguno" means "a certain":
* Ningún: This means "no" or "not any" and can be used to express the opposite of "a certain".
* Otro: This means "another" and can be used to indicate a different option from "a certain" one.
Examples:
* Alguno de los estudiantes fue a la fiesta. (Some of the students went to the party.)
* Ninguno de los estudiantes fue a la fiesta. (None of the students went to the party.)
* ¿Hay alguna** persona aquí? (Is there anyone here?)
* No hay ninguna** persona aquí. (There is no one here.)
* Hay alguno** libro en la mesa. (There is a certain book on the table.)
* No hay ningún** libro en la mesa. (There is no book on the table.)
The best antonym for "alguno" will depend on the specific context and the meaning you want to convey.