We established early on that becoming a leader does not ensure that you become the fount of all wisdom. That being true, you’re bound to face a question where you simply don’t know the answer. Don’t panic.
First, think through the question again to determine if you’ve been asked a fact question or an opinion question. If you’ve been asked an opinion question, you have to answer. You’re the leader; you’re expected to have opinions. If you’ve actually never thought through this particular issue, you can say, "Good question. I’ve never been asked that before. Let me think for a moment and come back to this one." Then your obligation is to return to the topic and express your opinion.
If you’ve been asked a fact question, and you don’t know the answer, don’t (under any circumstances) make up an answer. Your credibility as a leader as well as your reputation in your area of expertise will plummet faster than you can imagine when you’re found out (and you will be). In this situation, simply reply, "I don’t know, but I’ll check the facts and get back to you." Now your obligation is to do what you promised. Check the facts and get back to the person who asked the question. Your reputation will be enhanced as long as you follow through.