Electron rest mass is the mass of a stationary electron. It is denoted by the symbol me. The value is about 9.11×10-31/n kilograms. It is related to the Avogadro constant. It is also called as invariant mass. The 'rest mass' of an object is the inertial mass of an object, when it is at rest. The rest mass of helion is M(he) =4.002603u. On splitting its constituent particles, which is 2protons, 2 nuetrons, 2 electrons, they have the following masses as M(p)= 1.007276, M(n)=1.008665, M(e)= .000548 u.