Salem investigates the reaction of 5 different metals with diluted nitric acid, which variable should he changes in his investigation? * concentration of the acid
mass of the metals
volume of the acid
type of the metal

C) electrons encircling a nucleus with neutrons and protons

Is there any options, for this

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.