When Mg(s) is added to HCl(aq), which gas is produced?

• A. Oxygen (O_2)
• B. Hydrogen (H_2)
• C. Nitrogen (N_2)
• D. Carbon dioxide (CO_2)

Answer: (B)

Verified step by step guidance

1. Identify the reactants: solid magnesium (Mg) and aqueous hydrochloric acid (HCl).
2. Recall that magnesium is a metal that reacts with acids to produce a salt and a gas.
3. Write the general reaction of a metal with an acid: \(\text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen gas}\).
4. Apply this to magnesium and hydrochloric acid: \(\mathrm{Mg(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{MgCl_2(aq)} + \mathrm{H_2(g)}\).
5. From the balanced equation, observe that the gas produced is hydrogen gas, \(\mathrm{H_2}\).