We know that an alpha particle consists of two protons and two neutrons.

Mass of proton = 1.007276 u

Mass of neutron = 1.008665 u

Where u = 1.6605402 × 10^-27 kg (Atomic mass unit)

Let the mass of the alpha particle be M

∴ Mass defect is ΔM,

Given, Binding energy = 28.2 MeV

Binding energy is also equal to

So,

[Note ]

Hence, the mass of an alpha particle is 4.0016u