During nuclear fusion, it is observed that when two hydrogen atoms are fused together to form one helium atom, there is a loss in mass, M. The atomic masses of one hydrogen atom and one helium atom are given in the table below. The masses are given in atomic mass unit (u).

1. Find the mass of two hydrogen atoms and subtract the mass of one helium atom.

Mass of two hydrogen atoms:
$2 \times 2.0141 = 4.0282\text{ u}$
Mass lost:
$M = 4.0282 - 4.0026 = 0.0256\text{ u}$

2. Write the mass loss in standard form.

$0.0256 = 2.56 \times 10^{-2}$

1. Form the percentage using mass loss as a fraction of the helium atomic mass.

From part (a), $M=2.56\times 10^{-2}=0.0256$ u.

$\text{Percentage}=\frac{M}{\text{atomic mass of one helium atom}}\times 100\%$

$=\frac{0.0256}{4.0026}\times 100\%$

2. Calculate and round the percentage appropriately.

$\frac{0.0256}{4.0026}\times 100=0.639584\ldots$

$\approx 0.640$

1. Convert the mass loss from atomic mass units to kilograms.

From part (a),
$M=2.56\times 10^{-2}\text{ u}.$
Given $1\text{ u}=1.66\times 10^{-27}\text{ kg}$,
$M=(2.56\times 10^{-2})(1.66\times 10^{-27})$
$=4.2496\times 10^{-29}\text{ kg}$
$\approx 4.25\times 10^{-29}\text{ kg}.$