which of these reactions are redox reactions? check all that apply.\ncd + hcl → cdcl₂ + h₂\ncucl₂ + na₂s →…

Explanation:

Step1: Recall redox reaction definition

A redox reaction involves oxidation - reduction, i.e., a change in oxidation states of elements.

Step2: Analyze reaction 1: (Cd + 2HCl\rightarrow CdCl_{2}+H_{2})

Cd goes from 0 to + 2 oxidation state (oxidation) and H goes from + 1 to 0 (reduction). So it is a redox reaction.

Step3: Analyze reaction 2: (CuCl_{2}+Na_{2}S\rightarrow 2NaCl + CuS)

There is no change in oxidation states of elements. It is a double - displacement reaction, not a redox reaction.

Step4: Analyze reaction 3: (CaCO_{3}\rightarrow CaO + CO_{2})

No change in oxidation states of elements. It is a decomposition reaction, not a redox reaction.

Step5: Analyze reaction 4: (2ZnS+3O_{2}\rightarrow 2ZnO + 2SO_{2})

S goes from - 2 to + 4 oxidation state (oxidation) and O goes from 0 to - 2 (reduction). So it is a redox reaction.

Step6: Analyze reaction 5: (CH_{4}+2O_{2}\rightarrow CO_{2}+2H_{2}O)

C goes from - 4 to + 4 oxidation state (oxidation) and O goes from 0 to - 2 (reduction). So it is a redox reaction.

Answer:

Cd + HCl → CdCl₂ + H₂, 2ZnS + 3O₂ → 2ZnO + 2SO₂, CH₄ + 2O₂ → CO₂ + 2H₂O