Why is the total mass of a helium nucleus not equal to the mass of its individual parts?

The "missing" mass is due to inaccurate measurement on a very small scale.

The "missing" mass has been converted to energy.

The "missing" matter has been converted to mass.

The "missing" mass has been converted to matter.

Question

Why is the total mass of a helium nucleus not equal to the mass of its individual parts?

The "missing" mass is due to inaccurate measurement on a very small scale.

The "missing" mass has been converted to energy.

The "missing" matter has been converted to mass.

The "missing" mass has been converted to matter.

sillybilly123 · Answer

B) is yer answer, but $E$ and $m$ are the same thing, with $c^2$ as the conversion factor so this doesn't really help IMHO