Learn Turkish: Bu sıfır mı, dokuz mu? - Is this a zero or a nine?

In Turkish, you don't always need a word for "or" when asking a question with two choices. Instead, you just put a question particle after each option. Sıfır mı, dokuz mu? acts like "Zero? Nine?" which translates perfectly to "a zero or a nine?".

Why does the question particle change from mı to mu?

This is because of 4-way vowel harmony. The question particle changes its vowel to match the last vowel of the word right before it. Sıfır has the undotted vowel ı, so it takes mı. Dokuz has the rounded vowel u, so it takes mu.

Is sıfır a number just like the ones in this lesson?

Yes, sıfır means zero! Even though counting usually starts from one, zero behaves exactly like the numbers 1-10. Here, it is being used as a noun to identify the written digit itself.

Why doesn't the Turkish sentence use a word for "a" (like bir) before the numbers?

In English, we often say "a zero" or "a nine" when looking at a single written digit. In Turkish, you do not need to add bir (a/an/one) in this context. The numbers themselves act as the nouns.