Question

which reactions are redox reactions?
check all that apply.
4k(s) + o₂(g) → 2k₂o(s)
al(s) + 3ag⁺(aq) → al³⁺(aq) + 3ag(s)
mg(s) + br₂(l) → mgbr₂(s)
so₃(g) + h₂o(l) → h₂so₄(aq)

Explanation:

Step1: Recall redox reaction definition

A redox reaction involves electron transfer (change in oxidation states).

Step2: Analyze reaction 1: \(4\text{K}(s) + \text{O}_2(g)

ightarrow 2\text{K}_2\text{O}(s)\)
K: 0 → +1 (oxidation, loses e⁻); O: 0 → -2 (reduction, gains e⁻). Redox.

Step3: Analyze reaction 2: \(\text{Al}(s) + 3\text{Ag}^+(aq)

ightarrow \text{Al}^{3+}(aq) + 3\text{Ag}(s)\)
Al: 0 → +3 (oxidation); Ag: +1 → 0 (reduction). Redox.

Step4: Analyze reaction 3: \(\text{Mg}(s) + \text{Br}_2(l)

ightarrow \text{MgBr}_2(s)\)
Mg: 0 → +2 (oxidation); Br: 0 → -1 (reduction). Redox.

Step5: Analyze reaction 4: \(\text{SO}_3(g) + \text{H}_2\text{O}(l)

ightarrow \text{H}_2\text{SO}_4(aq)\)
S: +6, O: -2, H: +1 (no oxidation state change). Not redox.

Answer:

A. \(4\text{K}(s) + \text{O}_2(g)
ightarrow 2\text{K}_2\text{O}(s)\), B. \(\text{Al}(s) + 3\text{Ag}^+(aq)
ightarrow \text{Al}^{3+}(aq) + 3\text{Ag}(s)\), C. \(\text{Mg}(s) + \text{Br}_2(l)
ightarrow \text{MgBr}_2(s)\)