The correct answer is actually B, "Cl2 is being oxidized."
To understand why, let's break down the reaction and the concept of oxidation and reduction.
In the given reaction, H2 (hydrogen gas) is reacting with Cl2 (chlorine gas) to form 2HCl (hydrogen chloride).
Oxidation is the process of losing electrons, while reduction is the process of gaining electrons. Oxidation and reduction always occur simultaneously and are referred to as redox reactions.
In this reaction, the chlorine atoms in Cl2 are each gaining one electron from one hydrogen atom to form 2HCl. This means that the chlorine atoms are being reduced (gaining electrons) from a state of 0 charge to -1 charge in HCl. Hence, choice A, "H2 is being reduced," is incorrect.
On the other hand, hydrogen atoms in H2 are each losing an electron to form H+ ions in HCl. This means that the hydrogen atoms are being oxidized (losing electrons) from a state of 0 charge to +1 charge in H+. Therefore, choice B, "Cl2 is being oxidized," is the correct answer.
Choice C, "H2 is gaining two electrons," does not accurately describe the reaction because hydrogen is gaining only one electron from each chlorine atom.
Finally, choice D, "Cl2 is acting as an oxidizing agent," is also incorrect because it implies that Cl2 is causing the oxidation of another species, which is not the case in this particular reaction.
Therefore, the correct answer is B, "Cl2 is being oxidized."