Here's why:

* Alpha decay involves the emission of an alpha particle, which is essentially a Helium nucleus (²⁴He).

* When an alpha particle is emitted, the atomic number of the parent nucleus decreases by 2, and the mass number decreases by 4.

* ²²⁰Rn has an atomic number of 86 and a mass number of 220.

* After alpha decay, the daughter product will have an atomic number of 84 (86 - 2) and a mass number of 216 (220 - 4).

* The element with atomic number 84 is Polonium (Po).

Therefore, the daughter product of alpha decay of ²²⁰Rn is ²¹⁶Po.