Answer: B. helium
Explanation:
Alpha decay: In this process, alpha particles is emitted when a heavier nuclei decays into lighter nuclei. The alpha particle released has a charge of +2 units.
General representation of an element is given as:[tex]_Z^A\textrm{X}[/tex] where,
Z represents Atomic number
A represents Mass number
X represents the symbol of an element
[tex]_Z^A\textrm{X}\rightarrow _{Z-2}^{A-4}+_2^4\alpha[/tex]
As the alpha particle has atomic number of 2 and mass number of 4, this is helium nuclei.
