What 1 - used in questions to ask for particular information about sb/sth: What is your name? What (= what job) does he do? What time is it? What kind of music do you like? 2- the thing or things that; whatever: What you need is a good meal. Nobody knows what will happen next. I spent what little time I had with my family. 3- used to say that you think that sth is especially good, bad, etc.: What awful weather! What a beautiful house!

Which 1- used in questions to ask sb to be exact about one or more people or things from a limited number: Which is better exercise—swimming or tennis? Which of the applicants has got the job? Which of the patients have recovered? Which way is the wind blowing? 2- used to be exact about the thing or things that you mean: Houses which overlook the lake cost more. It was a crisis for which she was totally unprepared.

What lo usas cuando solo hay una opción de respuesta. Digamos que quieres preguntarle el numero de telefono a un amigo: Le dirías What´s your phone number? Usas Which cuando hay más posibilidades de respuesta. Digamos que un amigo te da su dirección para que vallas a su casa, pero el problema es que su casa no tiene número: Para preguntarle cual de todas es Usarías "Which" porque hay muchas casas al rededor. Así que dirías Which is your house?