Which two chemicals are combined to produce hydrochloric acid (HCl) in the laboratory?

• A. Hydrogen gas (H2) and chlorine gas (Cl2)
• B. Hydrogen gas (H2) and sodium chloride (NaCl)
• C. Hydrogen peroxide (H2O2) and chlorine gas (Cl2)
• D. Sodium chloride (NaCl) and water (H2O)

Answer: (A)

Verified step by step guidance

1. Understand that hydrochloric acid (HCl) is a compound consisting of hydrogen and chlorine atoms bonded together.
2. Recall that in the laboratory, HCl gas can be produced by the direct combination of hydrogen gas (H\_2) and chlorine gas (Cl\_2) under appropriate conditions, such as exposure to light or heat.
3. Recognize that other options like sodium chloride (NaCl) and water (H\_2O) do not directly produce HCl gas; instead, NaCl dissolved in water forms hydrochloric acid solution, but this is not a direct synthesis of HCl gas.
4. Note that hydrogen peroxide (H\_2O\_2) and chlorine gas (Cl\_2) do not combine to form HCl; hydrogen peroxide is an oxidizing agent and reacts differently with chlorine.
5. Therefore, the correct chemical reaction to produce hydrochloric acid gas in the lab is the combination of hydrogen gas (H\_2) and chlorine gas (Cl\_2), which can be represented as: \(\mathrm{H_2 + Cl_2 \rightarrow 2HCl}\).