Suppose I want to write a sentence:

Why not a girl or woman? Because they are too emotional.

Is this a grammatically correct way to write it. The part "Because I have to study" is not a complete sentence so am i supposed to add a hyphen??? I totally made this sentence up just to get an idea of the grammatical concept.

Thanks!

*****the part "Because they are too emotional"

Informally, you're right.

However, in formal English, you'd need to say: Girls and women are too emotional.

Both parts that you have written are fragments. Simply putting them together won't solve anything.

The incompleteness of the meaning of the first part, though, makes it difficult to tell you what to do with this, though. To what is "Why not a girl or woman?" referring?

The sentence "Why not a girl or woman? Because they are too emotional" is grammatically correct. However, the second part "Because they are too emotional" is a dependent clause and not a complete sentence on its own. If you want to make it a complete sentence, you can add a subject to it, such as "I don't choose a girl or woman because they are too emotional."

Regarding your question about adding a hyphen, hyphens are not necessary in this case. Hyphens are used to join words together or to separate a word at the end of a line. They are not typically used to connect sentences or to make fragments complete. To make a fragment into a complete sentence, you usually need to add a subject and a predicate.