A covalent bond is one between two nonmetals, while an ionic bond is formed between a metal and a nonmetal. Covalent bonds also do not dissociate in aqueous solution to form cations and anions; this is a characteristic of ionic bonds. For example,  represents a bond between a metal () and a nonmetal (), and it dissociates in aqueous solution to form a cation () and an anion (). In contrast,  represents a bond between two nonmetals, and it does not dissociate in aqueous solution. Ionic compounds are also good conductors of electricity, while covalent compounds are not. This is because moving electrons are required in order to conduct electricity. When dissolved in aqueous solution, ions are free to move and thus conduct electricity. Covalent bonds have localized electrons, which cannot move and thus cannot conduct electricity well.

A covalent bond is a bond between two nonmetals, in which electrons are shared. This means that  cannot be the correct answer, as sodium is a metal. In fact,  is a classic example of an ionic compound.

A polar covalent bond is a bond between two nonmetals in which one nonmetal is more electronegative than the other, pulling the shared electrons toward itself. This occurs in ; chlorine is much more electronegative than hydrogen and pulls the shared electrons toward itself. This gives chlorine a partial negative charge and hydrogen a partial positive charge.  is also an example of a polar covalent bond; oxygen is much more electronegative than hydrogen, and each oxygen in a water molecule pulls the shared electrons toward itself. This gives oxygen a partial negative charge and hydrogen a partial positive charge. 

A nonpolar covalent bond is a bond between two nonmetals in which electrons are shared equally between the nonmetals. This occurs when the two nonmetals are of equal electronegativity. As the atoms of  have the same identity (chlorine), they have the same electronegativity. Thus, electrons are shared equally between the two chlorine atoms--in a nonpolar covalent bond.

For this question, we're asked to determine which answer choice represents a compound with a total of six covalent bonds.

To answer this, we'll need to know the structure of each of the compounds. Moreover, it's important to remember that double bonds count as two covalent bonds.

Both sulfuric acid and phosphoric acid have a total of eight covalent bonds, while nitric acid has five. Carbonic acid is the only one shown that contains six covalent bonds, making it the correct answer.

Dipole-dipole interactions are the weakest because they are the result of attractions between weak partial charges

Hydrogen bonds are a special type of dipole-dipole interaction, but they are much stronger. 

An ionic bond is the result of the complete transfer of electrons from on atom to another. This results in a positive charge on one atom and a negative charge on the other. The charges on these ions are much stronger than in dipoles. The two oppositely charged atoms are held together by electrostatic attraction.  

Atoms that are part of a covalent bond share electrons. This makes the atoms harder to separate and, therefore, the bond is very strong.

Oxygen has a valence of 6, meaning it is looking to form two covalent bonds to complete its octet. Thus,  exists as a diatomic molecule joined by a double covalent bond.  and  are held together by single covalent bonds, and  is held together by a triple covalent bond.