Which of the following condition (s) is NOT an essential condition for a valid sale of property?

Consideration for the transfer can be money or in kind

The following are the essentials for a sale to be valid:
There should be two different parties- the seller and the buyer;
Both the parties should be competent to transfer;
The property to be transferred should be in existence;
Consideration for the transfer should be money;
The contract should be in accordance with law.