Question

To what element does polonium-208 (atomic number 84 decay when it emits an alpha particle?

Answer 1

Alpha decay means the element loses at Helium particle. Helium-4 (atomic number 2)

If polonium will lose 2 protons and 2 neutrons, it will become 204 mass, 82 atomic number. which is Lead (Pb). 

Answer 2

Answer: $_{82}^{204}\textrm {Pb}$

Explanation:-

Alpha Decay: In this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle or a helium nucleus.The atomic number gets reduced by 2 units and the mass number is reduced by 4 units.

General representation of an element is given as:$_Z^A\textrm{X}$

where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

The chemical equation for a alpha decay is represented as:

$_Z^A\textrm{X}\rightarrow _{Z-2}^{A-4}+_2^4\alpha$

$_{84}^{208}\textrm{Po}\rightarrow _{84-2}^{208-4}\textrm {Y}+_2^4\textrm{He}$

$_{84}^{208}\textrm{Po}\rightarrow _{82}^{204}\textrm {Pb}+_2^4\textrm{He}$