electron from a positively charged species than it will be to remove an electron from a neutral
version of the same species. In other words, the second ionization energy of an element is
always greater than its first ionization energy. Based on this fact alone, choices A, D, and E can
be eliminated. To choose between the remaining two choices, we must reason that a small
value for ionization energy corresponds to relative ease of removal of the electron. A Group IA
metal atom loses its first electron with relative ease, but after that it will possess an electronic
configuration similar to that of a noble gas. It will therefore be difficult to remove another
electron, implying a high second ionization energy. Looking at the numbers in the table, we
see that both remaining choices have relatively small values for first ionization energy, but
that X has a much higher second ionization energy. It follows that element V is most likely a
Group IIA element (e.g., Mg, Ca) while element X is most likely a member of Group IA (e.g., Na,
K). Choice C, then, is the best choice.50 . A
Pressures are additive as described by Dalton’s law of partial pressures:40 torr + 140 torr = 180 torr51 . B
This question asks you to determine why water has a higher boiling point than hydrogen
fluoride. Choice B says that water has a higher boiling point because it can form more
hydrogen bonds. Hydrogen bonding does affect boiling points by increasing the attraction
between the molecules of a compound. Water is capable of forming as many as four hydrogen
bonds per molecule, while hydrogen fluoride can only form two. This intermolecular
attraction leads to a complexation of water molecules and contributes to the high boiling
point of water.
52 . A