Answer the following question given this paragraph: 

Chapter 2 1 The mass number is the total number of protons and neutrons in the nucleus of an atom. 3 The water hydrolyses, or breaks, the glycosidic bond, forming two monosaccharides. 4 D 6 A 8 B 10 C 12 B 14 A 16 C 18 A 20 B 22 D 24 B 26 A 28 B 30 D 32 B 33 These four elements—oxygen, carbon, hydrogen, and nitrogen—together make up more than 95 percent of the mass of the human body, and the body cannot make elements, so it is helpful to have them in consumables. 35 Magnesium’s 12 electrons are distributed as follows: two in the first shell, eight in the second shell, and two in its valence shell. According to the octet rule, magnesium is unstable (reactive) because its valence shell has just two electrons. It is therefore likely to participate in chemical reactions in which it donates two electrons. 37 Water is a polar molecule. It has a region of weakly positive charge and a region of weakly negative charge. These regions are attracted to ions as well as to other polar molecules. Oils are nonpolar, and are repelled by water. 39 It is not. An exchange reaction might be AB + CD → AC + BD or AB + CD → AD + BC . In all chemical reactions, including exchange reactions, the components of the reactants are identical to the components of the products. A component present among the reactants cannot disappear, nor can a component not present in the reactants suddenly appear in the products. 41 Lemon juice is one hundred times more acidic than orange juice. This means that lemon juice has a one hundred-fold greater concentration of hydrogen ions. 43 Maltose contains 12 atoms of carbon, but only 22 atoms of hydrogen and 11 atoms of oxygen, because a molecule of water is removed during its formation via dehydration synthesis.


Q: According to the octet rule, magnesium is unstable because its valence shell has just two of what?


A:
electrons