19. The valence electron configuration of an element is . To which group does X belong?
(A) Group 3A
(B) Group 4A
(C) Group 5A
(D) Group 6A
(E) Group 7A

15. From the following list of observations, choose the one that most clearly supports the conclusion that the mass of the atom is located mainly in the nucleus. (A) the emission spectrum of hydrogen (B) the photoelectric effect (C) the scattering of alpba particles by metal foil (D) diffraction (E) cathode "rays"

16. Which of the following is a reasonable criticism of the Bohr mode] of the atom? (A) it makes no attempt to explain why the negative electron does not eventually fall into the positive nucleus (B) it does not adequately predict the line spectrum of hydrogen (C) it does not adequately predict the ionization energy of the valence electron(s) for elements other than hydrogen (D) it does not adequately predict the ionization energy of the first-energy-level electrons for elements other than hydrogen (E) it shows the electrons to exist outside of the nucleus

17. Which of the following is not determined by the principal quantum number, n, of the electron in a hydrogen atom? (A) the energy of the electron (B) the minin mum wavelength of the light needed to remove the electron from the atorn (C) the size of the corresponding atomic orbital(s) (D) the shape of the corresponding atomic orbital(s) (E) all of the above are determined by n

18. Which of the following statements is false? (A) an orbital can accommodate at most two electrons (B) the electron density at a point is proportional to at that point (C) the spin quantum number of an electron must be either +1/2 or -1/2 (D) a 2p orbital is more penetrating than a 2s； that is, it has a higher clectron density near the nucleus and inside the charge cloud of a Is orbital (E) in the usual order of filling, the 6s orbital is filled before the 4f orbital

20. In a 0.1 molar solution of NaCl in water, which of the following will be closest to 0.1? (A) the mole fraction of NaCl (B) the mass fraction of NaCl (C) the mass percent of NaCl (D) the molality of NaCI (E) all of these are about 0.1

21. Which statement about hydrogen bonding is true? (A) hydrogen bonding is the intermolecular attractive forces between two hydrogen atoms in solution. (B) the hydrogen-bonding capabilities of water molecules cause CH3CH2CH2CH3； to be more soluble in water than is CHJOH (C) hydrogen bonding of solvent molecules with a solute will not affect the solubility of the solute (D) hydrogen-bonding interactions between molecules are stronger than the covalent bonds within the molecule (E) hydrogen bonding arises from the dipole moment created by the unequal sharing of electrons in certain covalent bonds within a molecule

22. A solution of two liquids, A and B, shows negative deviation from Raoult's law. This means that (A) molecules of A interact strongly with other A-type molecules (B) the two liquids have a positive heat of solution (C) molecules of A interact weakly, if at all, with B molecules (D) the molecules of A hinder the strong interaction between B molecules (E) molecules of A interact more strongly with B than with A or and more strongly than B with B

23. Which of the following will cause the calculated molar mass of a compound determined by the freezing-point depression method to be greater than the true molar mass? (A) water gets into the solvent after the freezing point of the pure solvent is determined (B) some of the solute molecules break apart (C) the mass of solvent is smaller than determined from the weighing (D) while adding the solute, the technician spilled some of it on the lab bench (E) all of these

24. A cucumber is placed in a concentrated salt solution. What is most likely to happen? (A) water will flow from the cucu ucumber to the solution (B) water will flow from the solution to the cucumber (C) salt will fow into the cucumber (D) salt will precipitate out (E) no change will occur

25. The phrase "a solid dissolved in a gas" describes a(n) (A) foam (B) sol (C) emulsion (D) aerosol (E) none of these