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"

11. Which statement is true of a process in which 1 mol of a gas is expanded from state A to state B? (A) when the gas expands from state A to state B, the surroundings are doing work on the system (B) the amount of work done in the process must be the same, regardless of the path (C) it is not possible to have more than one path for a change of state (D) the final volume of the gas will depend on the path taken (E) the amount of heat released in the process will depend on the path taken

12. Which of the following statements is correct? (A) the intemal energy of a system increases when more work is done by the system than heat is flowing into the system (B) the internal energy of a system decreases when work is done on the system and heat is flowing into the system (C) the system does work on the surroundings when an ideal gas expands against a constant external pressure (D) all the statements are true (E) all the statements are false

13. For the vaporization of a liquid at a given pressure, (A) △G is positive at all temperatures (B) △G is negative at all temperatures (C) △G is positive at low temperatures but negative at high temperatures (and zero at some temperature) (D) △G is negative at low temperatures but positive at high temperatures (and zero at some temperature) (E) none of above

14. is _______ for exothermic reactions and _______ for endothermic reactions. (A) favorablc, unfavorable (B) unfavorable, favorable (C) favorable, favorable (D) unfavorable, unfavorable(E) cannot tell

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

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

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