I think the correct answer from the choices listed above is option B. When a substance changes from one phase to another, the average kinetic energy of the substance <span>changes since the molecules movements are changed as well. Hope this answers the question. Have a nice day.</span>
Answer: The atomic mass of this element in atomic mass units is 20.3
Explanation:
According to avogadro's law, 1 mole of every substance weighs equal to molecular mass and contains avogadro's number
of particles.
To calculate the number of moles, we use the equation:
Let atomic mass of element is X amu
atoms weigh = X amu
1 atom weigh = 

Atomic mass of this element in atomic mass units is 20.3