Explain with reasons, whether a valid contract has been formed under the Contracts Act 1950, in the following situations:

1. Kelly and Nana wrote to each other on the same day. Kelly offered to buy Nana's pearl ring for RM1,000, Nana offered to sell the same at the same price. Will Kelly be able to enforce the resulting 'contract'? Give reasons for your answer.
2. Last January, Adam and Cindy made an agreement whereby Adam is to give Cindy a diamond brooch by way of a gift by 1 February 2020. It is now March 2020 but Adam has not given Cindy the brooch. Can Cindy enforce Adam's promise?
3. Jim agrees to sell his car worth RM100,000 for RM100 to Charles. Jim's consent to the agreement was freely given. Can Jim challenge the validity of this transaction?
4. Tim wants to buy a new car and decides to sell one of his cars. He owns three cars, a Mercedes, a BMW and a Proton Perdana. Tim meets Alan and says, "I offer to sell you my car for RM100,000.00". Alan immediately accepts theoffer. Alan has now changed his mind and does not want to buy Tim's car. Advise Alan whether he can challenge the contract.
5. Will you answer differs if Tim offers Alan to sell his Proton Perdana for RM100,000.00, but Alan agrees thinking he had been offered the Mercedes.