1st QUESTION: What is the fundamental difference between closed-ended and open-ended questions?

Closed ones are for personal matters and open ones are for professional matters
Closed-ended questions limit the answer to "yes" or "no", while open-ended questions invite elaboration
Open ones are always shorter than closed ones
There is no fundamental difference between them

2nd QUESTION: What is the main purpose of a closed question?

It's an open question, and it's risky because it invites a long discussion
It's a powerful question, and it has no associated risk
It's a closed question, and it's risky because a monosyllabic answer can shut down the conversation
It's a development question, and it's risky because it demonstrates a lack of initiative