which two chemical equations show double - replacement reactions? a. ca(oh)2 + h2so4 → caso4 + 2h2o b. 2li +…

Brief Explanations:

A double - replacement reaction has the general form AB + CD → AD+CB. In option A, $\text{Ca(OH)}_2$ and $\text{H}_2\text{SO}_4$ react to form $\text{CaSO}_4$ and $\text{H}2\text{O}$ where the cations ($\text{Ca}^{2 +}$ and $\text{H}^+$) and anions ($\text{OH}^-$ and $\text{SO}{4}^{2 -}$) exchange partners. In option D, $\text{Na}_2\text{CO}_3$ and $\text{H}_2\text{S}$ react to form $\text{H}_2\text{CO}_3$ and $\text{Na}2\text{S}$ with the cations ($\text{Na}^+$ and $\text{H}^+$) and anions ($\text{CO}{3}^{2 -}$ and $\text{S}^{2 -}$) swapping. Option B is a single - replacement reaction and option C is a combination reaction.

Answer:

A. $\text{Ca(OH)}_2+\text{H}_2\text{SO}_4\rightarrow\text{CaSO}_4 + 2\text{H}_2\text{O}$, D. $\text{Na}_2\text{CO}_3+\text{H}_2\text{S}\rightarrow\text{H}_2\text{CO}_3+\text{Na}_2\text{S}$