When two hydrogen nuclei combine to form one helium nucleus, nuclear fusion has taken place.
true or false

Yes.  That's a nice, simple, intuitive description of the process that
liberates energy in the cores of stars and "H" bombs.

When 2 Hydrogen nuclei combine to form 1 Helium nucleus,
the combined nucleus has about 0.7% less mass than the
Hydrogen nuclei had.  That "missing mass" shows up in the
form of energy leaving the site of the fusion.
Can you say "big boom" ?

How many calories in food