En cual also correct?

Question

For the following question, is en cuál also correct? 
La casa ________ ha sido derrumbada. 
The house which I was so happy in has been demolished.que fui tan felizen la que fui tan felizla cual fui tan feliz enen cual fui tan feliz

Silvia Piriz · Accepted Answer

Hola Devin P.
In this sentence, you are not allowed to use “en cuál” on its own. In Spanish, when a relative clause needs a preposition (like “in”, “with”, “on”), the preposition must be placed before the relative pronoun, not left at the end of the sentence the way English allows.
In English you can say:
The house which I was so happy in has been demolished.
But in Spanish the preposition must move to the front:
La casa en la que fui tan feliz ha sido derrumbada.
La casa en la cual fui tan feliz ha sido derrumbada. (more formal)
This is the only way to express “in which”. You cannot write just “La casa en cuál…” — that is not grammatical.
If the “en la que…” part is not meant to go in the blank but somewhere else in the sentence, then the blank must be filled with just que / la cual, without “en”.
So the rule is:

You cannot say “en cuál” alone in this context.

You must either use the full structure “en la que / en la cual” when the preposition belongs there, or omit “en” entirely if the prepositional phrase appears elsewhere.

Saludos
Silvia