9.2 x 10⁴ mol Ar (39.95g) =

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The total number of nucleons

In any atom of any element, you will find protons and neutrons in the nucleus of any atom 

I'd say your answer would be the sides of a metal pan become hot when the pan is placed on the stove burner

The internal energy of the system we can term it as total potential energy and kinetic energy. energy flows out of the surrounding from the system then we can say that the internal energy of the final state is lower than its initials. the sign of  δesystem is negative.δesystem = efinal - einitial=-ve  efinal  ∠einitial.