To determine which chemical reaction involves the production of a gas, we need to examine each of the given reactions:
1. [tex]\(2 \text{Li (s)} + \text{F}_2 \text{(g)} \rightarrow 2 \text{LiF (s)}\)[/tex]
This reaction involves the combination of lithium (solid) and fluorine gas to produce lithium fluoride (solid). There is no gas produced in this reaction.
2. [tex]\(\text{Zn (s)} + 2 \text{HCl (aq)} \rightarrow \text{H}_2 \text{(g)} + \text{ZnCl}_2 \text{(aq)}\)[/tex]
This reaction involves zinc (solid) reacting with hydrochloric acid (aqueous) to produce hydrogen gas and zinc chloride (aqueous). The production of [tex]\( \text{H}_2 \text{(g)} \)[/tex] indicates that a gas is produced in this reaction.
3. [tex]\(\text{HNO}_3 \text{(l)} + \text{H}_2 \text{O (l)} \rightarrow \text{H}_3 \text{O}^+ \text{(aq)} + \text{NO}_3^- \text{(aq)}\)[/tex]
This reaction involves nitric acid (liquid) reacting with water (liquid) to produce hydronium ions (aqueous) and nitrate ions (aqueous). There is no gas produced in this reaction.
4. [tex]\(\text{K}_2 \text{CrO}_4 \text{(aq)} + \text{Ba} \left( \text{NO}_3\right)_2 \text{(aq)} \rightarrow \text{BaCrO}_4 \text{(s)} + 2 \text{KNO}_3 \text{(aq)}\)[/tex]
This reaction involves potassium chromate (aqueous) reacting with barium nitrate (aqueous) to produce barium chromate (solid) and potassium nitrate (aqueous). There is no gas produced in this reaction.
After examining all the reactions, it is clear that the second reaction:
[tex]\[ \text{Zn (s)} + 2 \text{HCl (aq)} \rightarrow \text{H}_2 \text{(g)} + \text{ZnCl}_2 \text{(aq)} \][/tex]
involves the production of hydrogen gas ([tex]\(\text{H}_2 \text{(g)}\)[/tex]). Hence, the correct answer is the second chemical reaction.
