Question: In the term trace element, the adjective trace means that

Answer: the element is required in very small amounts.

Question: Compared with 31P, the radioactive isotope 32P has

Answer: one more neutron.

Question: The reactivity of an atom arises from

Answer: the existence of unpaired electrons in the valence shell.

Question: Which statement is true of all atoms that are anions?

Answer: The atom has more electrons than protons.

Question: Which of the following statements correctly describes any chemical reaction that has reached equilibrium?

Answer: The rates of the forward and reverse reactions are equal.

Question: We can represent atoms by listing the number of protons, neutrons, and electrons-for example, 2p+, 2n0, 2e- for helium. Which of the following represents the 18O isotope of oxygen?

Answer: 8p+, 10n0, 8e-

Question: The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound.

Answer: H2S

Question: What coefficients must be placed in the following blanks so that all atoms are accounted for in the products? C6H12O6 S _____ C2H6O + _____ CO2

Answer: 2; 2

Question: Which of the following four statements, if any, is true regarding essential elements and living organisms?

Answer: Although all forms of life require iron, other elements are required only by certain species.

Question: Consider this statement: Concentrations of trace elements in an environment above what is required by organisms generally have no effect on those organisms. Which of the following is a valid response to this statement?

Answer: False. Elevated concentrations of some trace elements such as cobalt and chromium can be toxic.