If a student asks you a question and you don't know the exact answer , what will you do ?

A 'Smart' Question indeed! Thank you so much Mr. Ramy Ehab for initiating such a Constructive discussion.

In such a scenario;

1)  I would FRANKLY ADMIT THAT I DON'T KNOW THE ANSWER TO THAT PARTICULAR QUESTION.

2)  Then, I would ask all students if anyone knows the Answer to that Question, he/she must share that with the whole Class.

3)  Consequently, I would THANK the student before the WHOLE CLASS who initiated such a “BRAINSTORMING QUESTION” and also PRAISE the student who “ANSWERED that QUESTION” and will ask the class to “CLAP for BOTH OF THEM” as a token of APPRECIATION. 

Without any prejudice , you must appreciate the question with a big smile and honestly accept that the question apparently seems to be a little trivial,  and tell the class that be prepared to discuss the matter/problem elaborately in the subsequent lecture session..:-) after all a teacher is also an avid learner and it is a endless  process.....;-)

All the human are not perfect in knowledge. I will excuse and will take time to get the answer and let him know as soon as possible. 

It's okay to say I do not know, but it is a lie that makes up an answer

i will teach this to students

I will ask for an internet search under that question title

if i dont know the answer then i will accept that i dont know the answer but i will tell them tomorrow.