The question asks us to identify the common element in the transactions of a gift, settlement, and will. Let's analyze each option to determine the correct answer:

1. Physical delivery of possession: This is not necessarily present in all three transactions. A gift may involve physical delivery, but settlements and wills can convey interest without immediate physical transfer.
2. Absence of consideration: While gifts and wills typically do not involve consideration, some settlements might involve consideration. Therefore, this is not common to all three.
3. Voluntary disposition: Each of these transactions involves voluntary action on the part of the donor, settlor, or testator. In a gift, the donor voluntarily transfers property without expecting anything in return. In a settlement, the settlor voluntarily disposes of property for distribution. In a will, the testator voluntarily allocates their property to take effect upon death.
4. Vesting of the right in praesenti: This occurs when rights are vested immediately, but wills often vest rights in the future. Therefore, this is not common to all the transactions.

The correct answer is voluntary disposition. This is the element common to all three transactions as they all involve voluntary action on the part of the person executing the instrument. Each transaction, whether it is a gift, settlement, or will, involves the individual voluntarily deciding how their property or interests are to be disposed or allocated.

This aligns with the legal reasoning in the case of NP Saseendran v NP Ponnamma where it is detailed that the nature of a document or transaction is derived from its intention and is often a composite of settlement and will, involving voluntary disposition as a key element.