What is the dependent clause in this sentence If I can't find my mittens, I can't go out.

If I can't find my mittens ...

Explanation:

It's considered dependent (or subordinating) because it is a clause that cannot stand on it own; it's dependent on the main (independent) sentence.

Generally speaking, clauses that begin with adverbs are dependent clauses.

Ex.

After I graduate ...

When I die ...

If I win the lottery ...

I can't go out.

Explanation:

This the dependent clause because you not being able to go out depends on you finding your mittens.