Lime water turns milky when ...... gas is passed through it. The process of cellular respiration is .......... reaction.

Here are the solutions to the problems:

Question 47: Lime water turns milky when ...... gas is passed through it.

Lime water is a solution of calcium hydroxide, $\text{Ca(OH)}_2$. It turns milky due to the formation of an insoluble white precipitate, calcium carbonate ($\text{CaCO}_3$), when carbon dioxide ($\text{CO}_2$) gas is passed through it.
The chemical reaction is:

$$\text{Ca(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)}$$

While sulfur dioxide ($\text{SO}_2$) can also turn lime water milky by forming calcium sulfite ($\text{CaSO}_3$), carbon dioxide is the most common and characteristic gas associated with this test in general chemistry.

The final answer is $\boxed{\text{C. CO}_2}$.

Question 48: The process of cellular respiration is .......... reaction.

Cellular respiration is the metabolic process by which organisms convert nutrients into adenosine triphosphate (ATP) and then release waste products. In this process, glucose is oxidized, and oxygen is reduced.
The overall equation for aerobic cellular respiration is:

$$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy (ATP)}$$

• Endothermic reactions absorb energy, but cellular respiration releases energy (it is exothermic).
• Reduction is a part of a redox reaction where electrons are gained. While oxygen is reduced in cellular respiration, the entire process is not simply a reduction.
• Redox (reduction-oxidation) reactions involve the transfer of electrons. In cellular respiration, glucose is oxidized (loses electrons), and oxygen is reduced (gains electrons). Therefore, it is a redox reaction.
• Decomposition reactions involve a single compound breaking down into two or more simpler substances. Cellular respiration involves glucose reacting with oxygen, which is not a simple decomposition.

The final answer is $\boxed{\text{C. redox}}$.