Which one of the following is an oxyacid? (a) \(\mathrm{H}_{3} \mathrm{PO}_{3}\) (b) \(\mathrm{Mg}(\mathrm{OH})_{2}\) (c) \(\mathrm{Ba}(\mathrm{OH})_{2}\) (d) \(\mathrm{HCl}\)

In chemistry, an oxyacid is a type of acid that contains an oxygen atom. More specifically, an oxyacid includes a hydrogen atom, an oxygen atom, and at least one other element, typically a nonmetal. The defining characteristic of an oxyacid is that the hydrogen is directly bonded to the oxygen, which is in turn bonded to another nonmetal element. This bonding pattern is key to classifying a compound as an oxyacid.

For example, sulfuric acid (H_{2}SO_{4}) is an oxyacid because it has hydrogen atoms bonded to oxygen atoms, and these oxygen atoms are also bonded to the central sulfur atom. Contrarily, compounds lacking this specific arrangement do not qualify as oxyacids, even if they contain the same elements. Understanding the structure of an oxyacid is essential for recognizing and naming these compounds in chemistry.

To identify an oxyacid among various compounds, it's important to look at the chemical structure for the presence of a specific bond sequence: hydrogen to oxygen, and that oxygen to another nonmetal. The compound should contain at least one hydrogen atom bonded to oxygen, and this oxygen should be part of a group bonded to a nonmetal, such as phosphorus, sulfur, or chlorine.

Going through the provided exercise options, the correct identification process involves:

• Checking for hydrogen (H) and oxygen (O) in the compound.
• Looking for the connection between these elements, ensuring hydrogen is bonded to oxygen.
• Confirming that the oxygen is also bonded to a nonmetal element.

H_{3}PO_{3}, with hydrogen bonded to oxygen and oxygen bonded to phosphorus, fits the correct pattern of an oxyacid. However, compounds like Mg(OH)_{2} and Ba(OH)_{2}, which are hydroxides, along with HCl, a binary acid, do not exhibit the structure of an oxyacid.

Understanding the distinction between oxyacids and hydroxides is crucial in chemistry. Oxyacids consist of hydrogen bonded to oxygen, with that oxygen also bonded to a nonmetal, as seen in H_{2}SO_{4} (sulfuric acid). In contrast, hydroxides feature a metal bonded to a hydroxyl group (OH), rather than to oxygen that is also bonded to hydrogen.

For example, Mg(OH)_{2} (magnesium hydroxide) and Ba(OH)_{2} (barium hydroxide) represent hydroxides due to the presence of metal (magnesium or barium in these cases) directly bonded to the hydroxyl group. Hydroxides generally signify the bases in acid-base chemistry while oxyacids characterize the acidic compounds. By comparing their structures, one can easily differentiate between these two classes of compounds and understand their distinct chemical behaviors.