Answer: H₂.
- A O₂
- B H₂
- C SO₂
- D H₂SO₄ vapour
Correct answer: B. H₂
Explanation: H⁺ ions are reduced at cathode: 2H⁺ + 2e⁻ → H₂. Hydrogen gas evolves.
In a Daniell cell, electrons flow externally from the zinc anode (oxidation) through the voltmeter to the copper cathode (reduction), while the salt bridge completes the circuit.
Concept context
Explore the link between chemical reactions and electricity. Covers galvanic cells, electrolysis, standard electrode potentials, the Nernst equation, and real-world applications like batteries and corrosion.