13. Which of the following equations represents an oxidation-reduction reaction? NaOH(aq)+HCl(aq)rightarrow NaCl(aq)+H_(2)O(l) Mg(s)+ZnCl_(2)(aq)rightarrow Zn(s)+MgCl_(2)(aq) 2HCl(aq)+Ba(OH)_(2)(aq)rightarrow BaCl_(2)(aq)+2H_(2)O(l) 2AgNO_(3)(aq)+Na_(2)CrO_(4)(aq)rightarrow Ag_(2)CrO_(4)(s)+2NaNO_(3)

oxidation-reduction (redox) reaction involves the transfer of electrons between two species, resulting in a change in oxidation states. To identify which equation represents a redox reaction, we need to examine the oxidation states of the elements involved in each reaction.<br /><br />1. **$NaOH(aq) + HCl(aq) \leftrightarrow NaCl(aq) + H_2O(l)$** <br /> - In this reaction, sodium (Na), hydrogen (H), chlorine (Cl), and oxygen (O) maintain their oxidation states throughout the reaction. There is no transfer of electrons, so this is not a redox reaction.<br /><br />2. **$Mg(s) + ZnCl_2(aq) \leftrightarrow Zn(s) + MgCl_2(aq)$** <br /> - Here, magnesium (Mg) starts with an oxidation state of 0 and ends up as Mg²⁺ in MgCl₂, indicating it has lost electrons (oxidation). Zinc (Zn) starts as Zn²⁺ in ZnCl₂ and ends up as elemental Zn with an oxidation state of 0, indicating it has gained electrons (reduction). This is a redox reaction.<br /><br />3. **$2HCl(aq) + Ba(OH)_2(aq) \leftrightarrow BaCl_2(aq) + 2H_2O(l)$** <br /> - In this reaction, all elements retain their oxidation states. There is no electron transfer, so this is not a redox reaction.<br /><br />4. **$2AgNO_3(aq) + Na_2CrO_4(aq) \leftrightarrow Ag_2CrO_4(s) + 2NaNO_3$** <br /> - In this reaction, silver (Ag), sodium (Na), chromium (Cr), nitrogen (N), and oxygen (O) do not change their oxidation states. There is no electron transfer, so this is not a redox reaction.<br /><br />Therefore, the equation that represents an oxidation-reduction reaction is:<br /><br />**$Mg(s) + ZnCl_2(aq) \leftrightarrow Zn(s) + MgCl_2(aq)$**