Which of the following reactions is a redox reaction?

• A. 2H2 + O2 → 2H2O
• B. AgNO3 + NaCl → AgCl + NaNO3
• C. HCl + NaOH → NaCl + H2O
• D. Ba(NO3)2 + K2SO4 → BaSO4 + 2KNO3

Answer: (A)

Verified step by step guidance

1. Identify the definition of a redox reaction: A redox (reduction-oxidation) reaction involves the transfer of electrons between two species, resulting in changes in their oxidation states.
2. Examine the first reaction: 2H2 + O2 → 2H2O. Determine the oxidation states of hydrogen and oxygen in the reactants and products. Hydrogen goes from 0 in H2 to +1 in H2O, and oxygen goes from 0 in O2 to -2 in H2O, indicating a change in oxidation states.
3. Examine the second reaction: AgNO3 + NaCl → AgCl + NaNO3. Check the oxidation states of all elements. Silver (Ag) remains +1, nitrate (NO3) remains -1, sodium (Na) remains +1, and chloride (Cl) remains -1. No change in oxidation states occurs.
4. Examine the third reaction: HCl + NaOH → NaCl + H2O. Check the oxidation states of all elements. Hydrogen, chlorine, sodium, and oxygen maintain their oxidation states throughout the reaction, indicating no electron transfer.
5. Examine the fourth reaction: Ba(NO3)2 + K2SO4 → BaSO4 + 2KNO3. Check the oxidation states of all elements. Barium (Ba), nitrate (NO3), potassium (K), and sulfate (SO4) maintain their oxidation states, indicating no electron transfer.