Alice offers Jack her car for HK$9000 and Jack replies by saying “I will take your car, but I will pay only HK$6000 for it" Is it a binding contract between Alice and Jack?
No, there is no binding contract.
As Jack has made a counter-offer of 6,000 instead of accepting the term as offered by Alice for $9,000. This was a counter-offer. Offer and acceptance therefore did not match with each other.