A neutral 4He atom loses its two electrons to form an α-particle (a bare 4He nucleus). Taking the mass of one electron to be 0.00055u and neglecting energy-mass effects other than the lost electron mass, which of the following is the best estimate for the percentage decrease in mass when the neutral atom becomes an α-particle?
a) 0.055%
b) 0.0003%
c) 0.03%
d) 0.014%