The correct answer is B. Although the number of electrons and protons is identical in a neutral atom, a change in the number of electrons does not change the identity of the atom, while a change in the number of protons does. The sum of the protons and neutrons is the mass number.

The correct answer is A. The alkali metals, located in the first column of the periodic table, have one valence electron. They normally form ions by losing that electron, leaving the highest energy level empty.

A is the correct answer. Chemical changes involve changes in chemical bonds to form new substances. Only chemical changes can release or absorb energy. According to the law of conservation of mass, matter is neither created nor destroyed during a chemical or physical change. Only nuclear reactions affect the nucleus, not chemical or physical changes.

The correct answer is A. The activation energy of a chemical reaction is lowered by catalysts. The other choices are not correct because the activation energy can be either lower or higher than the energy of the reactants (kinetic or potential) depending on their temperature.

The correct answer is C. Each mole of calcium chloride dissolves to form 3 moles of ions: 1 mole of Ca2+ and two moles of Cl−. The equation to solve is: