Ich weiß nicht, ob ...
ob means "whether" or "if" (in the sense of uncertainty, not condition) - and it behaves exactly like weil and dass from Lesson 26: it's a subordinating conjunction, so the verb moves to the end of its clause.
Direct: Haben Sie einen Termin frei? (Do you have an appointment free?)
Indirect: Ich möchte fragen, ob Sie einen Termin frei haben. (I'd like to ask whether you have an appointment free.)
Notice: the direct question flips the verb to the front (Lesson 5's yes/no question rule). The indirect version wraps it in "ob," and the verb goes back to normal - but now moves to the end of the ob-clause, exactly like weil (Lesson 26).
It's softer and more natural in many contexts - especially combined with würde gerne (Lesson 65) or möchte (Lesson 11) for genuinely polite phone and email German:
Ich weiß nicht, ob das rezeptfrei ist. (I don't know whether that's over-the-counter - Lesson 68)
Können Sie mir sagen, ob der Vertrag automatisch verlängert wird? (Can you tell me whether the contract renews automatically? - Lesson 51)
Both can translate as "if" in English, but they're not interchangeable: ob means "whether" (uncertainty about a yes/no fact); wenn means "if/when" (a condition or a repeated/future event). "Ich weiß nicht, ob es regnet" (I don't know whether it's raining) vs. "Wenn es regnet, bleibe ich zu Hause" (If it rains, I'll stay home).
1. "I don't know whether that's over-the-counter." - Ich weiß nicht, ob das rezeptfrei ______.
2. What does "ob" mean?
3. Does the verb move to the end after "ob," like after "weil"?
4. Which word means "if/when" (condition), not "whether"?
5. In a direct yes/no question, where does the verb go?
Cross-checked against the Goethe-Institut A1 practice materials.
Want to practice turning a specific real question into a polite indirect one? Ask your teaching agent.