How many atoms are in 0.5 g helium (he)?

Well first you need to know the molar mass of He which is 4.0026g/mol and Avogadro’s number which is 6.022*10^23 (units). So the equation is

0.5gHe * mol/4.0026He *(6.022*10^23)He atoms/mol

=7.5*10^22 He atoms

Round to only one sig fig because 0.5g only has one

Final 8*10^22 He atoms

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.

Deposition is the transition of matter going from gas to solid without passing through the liquid phase.a.) gas—-> solid