Discussion

Which of the following options about Reaction I (R1) and Reaction II (R2) are correct ?

Reaction I (R1) : Reaction of slaked lime with carbon dioxide
Reaction II (R2) : Heating of calcium bicarbonate

Answer: D

The correct description is R1 is exothermic and R2 is a decomposition.

R1 is the lime-water reaction. Slaked lime reacts with carbon dioxide to form calcium carbonate and water, and heat is released:

\[ \begin{aligned} &\text{Ca(OH)}_{2} + \text{CO}_{2} \\ &\rightarrow \text{CaCO}_{3} + \text{H}_{2}\text{O} \end{aligned} \]

R2 breaks one compound into three on heating, which is a decomposition:

\[ \begin{aligned} &\text{Ca(HCO}_{3})_{2} \\ &\rightarrow \text{CaCO}_{3} + \text{H}_{2}\text{O} + \text{CO}_{2} \end{aligned} \]

R2 is not a combination, and R1 is neither endothermic nor a decomposition, which rules out the other three options.

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