To determine which of the given chemical equations represents a redox reaction, let's examine each option and identify any changes in the oxidation states of the elements.
### Option A:
[tex]\[ AgNO_3 + NaCl \rightarrow AgCl + NaNO_3 \][/tex]
- Silver (Ag) in [tex]\( AgNO_3 \)[/tex] has an oxidation state of +1.
- Silver (Ag) in [tex]\( AgCl \)[/tex] has an oxidation state of +1.
- Sodium (Na) and Chlorine (Cl) also retain their oxidation states of +1 and -1, respectively.
In this reaction, there are no changes in the oxidation states of any elements. Therefore, this is not a redox reaction.
### Option B:
[tex]\[ Ca(OH)_2 + H_2SO_4 \rightarrow CaSO_4 + 2 H_2O \][/tex]
- Calcium (Ca) in [tex]\( Ca(OH)_2 \)[/tex] has an oxidation state of +2.
- Calcium (Ca) in [tex]\( CaSO_4 \)[/tex] has an oxidation state of +2.
- Hydrogen (H) and Sulfur (S) also retain their oxidation states.
In this reaction, there are no changes in the oxidation states of any elements. Therefore, this is not a redox reaction.
### Option C:
[tex]\[ Na_2CO_3 + H_2S \rightarrow H_2CO_3 + Na_2S \][/tex]
- Sodium (Na) in [tex]\( Na_2CO_3 \)[/tex] has an oxidation state of +1.
- Sodium (Na) in [tex]\( Na_2S \)[/tex] has an oxidation state of +1.
- Carbon (C), Oxygen (O), and Sulfur (S) also retain their oxidation states.
In this reaction, there are no changes in the oxidation states of any elements. Therefore, this is not a redox reaction.
### Option D:
[tex]\[ 2 Li + MgCl_2 \rightarrow 2 LiCl + Mg \][/tex]
- Lithium (Li) in its elemental form has an oxidation state of 0.
- In [tex]\( LiCl \)[/tex], each Li has an oxidation state of +1.
- Magnesium (Mg) in [tex]\( MgCl_2 \)[/tex] has an oxidation state of +2.
- Magnesium (Mg) in its elemental form has an oxidation state of 0.
In this reaction, Lithium is oxidized from 0 to +1 and Magnesium is reduced from +2 to 0. Because there is a change in the oxidation states of the elements involved, this is a redox reaction.
### Conclusion
Therefore, the chemical equation that represents a redox reaction is:
Option D: [tex]\( 2 Li + MgCl_2 \rightarrow 2 LiCl + Mg \)[/tex]
