Which of the following compounds has covalent bonds?

Covalent bonds form when two atoms share electrons, typically occurring between nonmetals. In the case of HCl (hydrochloric acid), the bond between hydrogen and chlorine is a classic example of a covalent bond. Hydrogen, which has one electron in its outer shell, shares an electron with chlorine, which has seven valence electrons, to achieve a full outer shell.

In contrast, the other compounds listed are ionic in nature. NaCl (sodium chloride) forms when sodium donates an electron to chlorine, resulting in a positive sodium ion and a negative chloride ion that attract each other. MgO (magnesium oxide) involves magnesium giving two electrons to oxygen, forming Mg²⁺ and O²⁻ ions that are held together by ionic bonds. Similarly, Cs2O (cesium oxide) involves cesium losing electrons to oxygen, leading to ionic bonding as well.

This distinction is crucial in understanding the properties of the compounds, as covalent compounds like HCl generally have lower melting and boiling points compared to ionic compounds that form strong attractions between their charged ions.