The alkaline earth metals are the elements in group II, such as beryllium and magnesium. They want to have a complete octet in their outermost energy level, so they tend to lose two electrons to form the ionic state, which gives them the electron configuration of the noble gas in the previous energy level and thus a smaller ionic radius. Therefore, both statements are true and the second correctly explains the first.

Atomic radius tends to increase down a group due to the addition of new energy levels; however, it decreases across a period due to increased shielding and increased nuclear mass. For these reasons, the elements with the smallest atomic radii would be in the upper right corner of the periodic table.

Protons and neutrons both have masses of approximately 1 amu, whereas the mass of an electron is negligible. Therefore, the mass number is equal to the number of protons and neutrons, which is 31.

The task is to find the atom or ion with its first three energy levels completely filled. Argon is not an answer choice, which means that it must be one of the ions with an atomic number close to argon's atomic number. Recalling that a positive charge means electrons were lost from the outermost shell and that a negative charge means electrons were gained in the outermost shell, the only answer that works is .

The  sublevel contains three orbitals, whereas the other levels listed contain different numbers of orbitals. The  level has one orbital; the  level has five; the  level has seven; and there is no  sublevel.

 has three bonding pairs and one non-bonding pair, which is the geometry for trigonal pyramidal, not trigonal planar.

There are six electron domains in .  has five bonding and one nonbonding pairs of electrons. The electron domain geometry of  is octahedral. When a molecule has octahedral electron domain geometry and has five bonding and one nonbonding pairs, the molecular geometry is square pyramidal.

In order to answer the question, it is important to first determine what kind of bonding is occurring in order to properly name the molecule. When nitrogen and oxygen form an  molecule, electrons are shared between the atoms, so a covalent bond is formed.

Because a covalent bond is formed, we can determine that name of the molecule will be based on number of each atom in the molecule. There are two nitrogen atoms in the resulting molecule, so the prefix in front of the "nitrogen" part of the name will be "di-," meaning two. There are four oxygen atoms in the resulting molecule, so the prefix in front of the "oxygen" part of the name will be "tetra," meaning four.

The molecules names will be arranged alphabetically, and the second atom will have "-ide" as the suffix. Therefore, the correct answer is "dinitrogen tetroxide."

In order to answer this question correctly, it is important to have knowledge of the formation of ionic bonds, polyatomic ions, and the periodic table. First, it is important to notice that calcium ions and sulfate ions will form an ionic bond. Knowing this, it can be understood that valance electrons will be exchanged between the ions and therefore, oppositely charged ions that are attracted to each other will be formed.

Calcium is in the second column of the periodic table, so it will provide two ions to the sulfate polyatomic ion. This will form a calcium cation () and a sulfate polyatomic anion ().

One calcium ion provides two electrons, which are both accepted by a sulfate polyatomic ion, so the ratio of calcium ions used to sulfate polyatomic ions used is 1:1. This means that only one of each ion is needed to form the compound, making the formula .

Initially it may be tempting to write the formula as ; however, since both ions have a "2" subscript in this form, it is redundant to the formula in this way. Only one of each ion is needed to form the compound.

Physical properties are aspects of matter that can be observed and measured without changing it. Chemical properties measure the potential for undergoing a chemical change. How zinc reacts to acid and in moist air are both chemical properties because the zinc is undergoing chemical change in each environment. The color, density, and melting point of the zinc can all be observed without changing the nature of the matter, so these are physical properties of zinc.