Final answer:
The required element for a valid real estate sales contract is that it must be signed by the seller. This signature indicates the seller's agreement to the contract's terms, including the transfer of the property title.
Step-by-step explanation:
The question refers to the elements required for a valid real estate sales contract. In real estate transactions, certain conditions must be met for a contract to be considered legally binding. Among these conditions, one fundamental element is that it must be signed by the seller. This is because the seller is the party transferring ownership of the property, and their signature indicates their agreement to the terms and conditions of the sale, including the transfer of the title to the buyer. It is not expressly required that the contract provide for possession by the buyer, installment payments, or a metes and bounds description of the property for the contract to be valid. While these elements may be included in the contract, they are not mandatory for the contract's validity, unlike the seller's signature.