Final answer:
The compound from the provided choices that features a polar covalent bond is HCl, where the electrons are unequally shared due to the difference in electronegativity between hydrogen and chlorine.
Step-by-step explanation:
The compound that contains a polar covalent bond from the given options is HCl (hydrochloric acid). A polar covalent bond is characterized by unequal sharing of electrons between two atoms with different electronegativities. In HCl, chlorine has a significantly higher electronegativity than hydrogen, which leads to the electrons being more attracted to the chlorine atom, creating a dipole moment with a partial negative charge on the chlorine and a partial positive charge on the hydrogen.
It is important to differentiate between polar covalent bonds and ionic bonds. Compounds like NaF and MgO are primarily ionic, as they form from the transfer of electrons between atoms with a large difference in electronegativity, leading to the formation of ions. In contrast, compounds like O2 and Br2 involve nonpolar covalent bonds, as these diatomic molecules are composed of two atoms of the same element, resulting in equal sharing of electrons.