A synthesis reaction is a type of chemical reaction in which two or more simple substances combine to form a more complex product. The general form of a synthesis reaction can be expressed as:
[tex]\[ A + B \rightarrow AB \][/tex]
Now, let's analyze the given reactions individually:
1. [tex]\( 2 \text{HgO} \rightarrow 2 \text{Hg} + \text{O}_2 \)[/tex]
- This reaction involves the decomposition of mercury(II) oxide ([tex]\( \text{HgO} \)[/tex]) into mercury ([tex]\( \text{Hg} \)[/tex]) and oxygen ([tex]\( \text{O}_2 \)[/tex]). It is a decomposition reaction, not a synthesis reaction.
2. [tex]\( \text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3 \)[/tex]
- This reaction is a double displacement reaction where silver nitrate ([tex]\( \text{AgNO}_3 \)[/tex]) and sodium chloride ([tex]\( \text{NaCl} \)[/tex]) are exchanging ions to form silver chloride ([tex]\( \text{AgCl} \)[/tex]) and sodium nitrate ([tex]\( \text{NaNO}_3 \)[/tex]). It is not a synthesis reaction.
3. [tex]\( \text{HCl} + \text{NaHCO}_3 \rightarrow \text{H}_2 \text{O} + \text{CO}_2 + \text{NaCl} \)[/tex]
- This reaction involves hydrochloric acid ([tex]\( \text{HCl} \)[/tex]) reacting with sodium bicarbonate ([tex]\( \text{NaHCO}_3 \)[/tex]) to produce water ([tex]\( \text{H}_2 \text{O} \)[/tex]), carbon dioxide ([tex]\( \text{CO}_2 \)[/tex]), and sodium chloride ([tex]\( \text{NaCl} \)[/tex]). This reaction includes aspects of both double displacement and decomposition, but it is not a synthesis reaction.
4. [tex]\( 2 \text{Na} + \text{Cl}_2 \rightarrow 2 \text{NaCl} \)[/tex]
- This reaction involves sodium ([tex]\( \text{Na} \)[/tex]) reacting with chlorine gas ([tex]\( \text{Cl}_2 \)[/tex]) to form sodium chloride ([tex]\( \text{NaCl} \)[/tex]). Here, two simple substances (sodium and chlorine) combine to form a more complex product (sodium chloride). This matches the definition of a synthesis reaction.
Therefore, the reaction that is best described as a synthesis reaction is:
[tex]\[ 2 \text{Na} + \text{Cl}_2 \rightarrow 2 \text{NaCl} \][/tex]
And the corresponding answer is:
4
