We should first remember the difference between sulfate, sulfite, and sulfide. Sulfate is , sulfite is ` and sulfide is .

The only answer choices that could be right must have in them. We then need to see that barium usually has a charge of , as the periodic table shows us, and so we need a charge of to cancel that out. The answer is .

Ionic chemical compounds are always named with the metal before the non-metal. The correct way to name sodium chloride would be , and not , because sodium is the metal and chloride is the non-metal.

All the other examples have the metal before the non-metal. The other answer choices correspond to potassium chloride, magnesium sulfate, hydrogen chloride (hydrochloric acid), and calcium fluoride.

Because iron has multiple oxidation states, we need to follow the cation with the roman numeral that signifies how many electrons each iron ion has donated to oxygen. Since oxygen gains two electrons in order to satisfy its octet, the three oxygens will accept a total of six electrons from two iron atoms. This means that each iron must donate three electrons, so that each atom donates electrons equally. As a result, the name of the ionic compound is iron(III) oxide.

Another acceptable name for the compound would be ferric oxide. The term "ferric" refers to iron(III) and the term "ferrous" refers to iron (II).

When naming covalent compounds, it is important to use a prefix before each element in order to designate how many atoms are in the compound. One key exception is when you only have one atom at the beginning of the compound (such as in this question). You will never start a covalent compound with "mono-". The prefix for five is "penta-", so the name of this covalent compound is phosphorus pentafluoride. The name indicates that there is one phosphorus atom bound to five fluorine atoms.

The molecule is a molecular compound because it contains two non-metals; therefore, it contains no ionic bonds. We use prefixes to describe the subscript for each element in molecular compounds. The molecule in this question has a subscript of two for each of the elements, so the prefix di- should be added to both sulfur and chlorine.

For molecular compounds, we change the ending of the final element to -ide, giving us the name "disulfur dichloride."

It is important to note that "chlorate" has a separate meaning, and refers to the complex ion .

is a molecular compound (a compound that contains two non-metals), so we must name it according to the rules for naming molecular compounds. These are different from the rules to name ionic compounds.

In molecular compounds we use prefixes (mono-, di-, tri- etc) at the beginning of each element to indicate the subscript for the element; however, we only use the prefix mono- for the second element in the compound. Mononitrogen dioxide is an incorrect answer choice because the compound name will never begin with mono-. We also need to change the ending of the last element in molecular compounds to -ide. Together, the name becomes "nitrogen dioxide."

Nitrate refers to the complex ion . Nitrogen oxide is simply . Nitrous acid is also known as hydrogen nitrite, and is formed from a hydrogen ion and a nitrite ion with an ionic bond: .

Nitrogen monoxide, also known as nitric oxide or, differs from the other listed compounds in the group because it is a molecular compound (two non-metals). The elements nitrogen and oxygen both have high electronegativities and will create a covalent bond, sharing the electrons between the two nuclei.

All the other answer choices are ionic compounds, containing one cation (metal) and one anion (non-metal). The metals will have relatively low electronegativities, while the non-metals will have relatively high electronegativities. This difference will pull electrons away from the metal (forming a cation) and toward the non-metal (forming an anion). The result is an ionic bond.

is a molecular compound, composed entirely of non-metallic elements with covalent bonds. Normally, these compounds follow a specific set of naming rules that would lead to this compound being called "nitrogen trihydride," however this particular compounds is an exception to normal naming rules.

is an example of a molecular compound that is given a non-systematic common name. The common name for is ammonia. Ammonium is incorrect, and refers to the complex ion .

Other exceptions to the naming rules include water () and methane ().

is an binary ionic compound because it contains one cation species and one anion species, connected by ionic bonds. Compounds with this structure should be named according to the rules for naming binary ionic compounds, which differ from the rules for naming molecular compounds. For these types of compounds the cation (usually a metal) should be listed first and the anion (non-metal) should be listed second with the suffix -_ide_added to the end.

Answer choices containing prefixes (mono-, di-, tri- etc) are incorrect because prefixes should only be used when naming molecular compounds.

Answer choices containing roman numerals are incorrect because roman numerals are only used to designate the charge of the cation when the cation is a transition metal, which are generally capable of multiple oxidation states and require the charge designation to differentiate. Magnesium is and alkaline earth metal, not a transition metal, and will always have a charge of positive two.

Using the proper naming conventions, refers to magnesium chloride.

Since beryllium is a cation metal and phosphorus is a anion non-metal, they can be combined to create an ionic compound.

In ionic compounds, the cation is always written before the anion in the formula so answer choices with phosphorus as the first element ( and ) are incorrect.

Ionic compounds must have a net charge of zero. Beryllium is an alkaline earth metal and has a charge of , since it is a member of group 2. Phosphorus has a charge of since it is a member of group 15. To create a molecule with a net charge of zero there must be three beryllium ions for every two phosphorus ions.

is not a correct answer choice because the net charge of the molecule does no equal zero.

is the balanced ionic formula for beryllium phosphate, but contains oxygen as well as beryllium and phosphorus.