A compound which can be used in space vehicles both to absorb $CO_{2}$ and liberate $O_{2}$ is:

Question

Accepted Answer

Option 3, $Na_{2}O_{2}$ (sodium peroxide), is the correct answer for a compound that can be used in space vehicles both to absorb $CO_{2}$ and liberate $O_{2}$. Here's why:

1. **Explanation for Option 3 ($Na_{2}O_{2}$):**
   - Sodium peroxide ($Na_{2}O_{2}$) is a compound that reacts with carbon dioxide ($CO_{2}$) to form sodium carbonate ($Na_{2}CO_{3}$) and oxygen ($O_{2}$). The reaction is as follows:
     $$
     2Na_{2}O_{2} + 2CO_{2} \rightarrow 2Na_{2}CO_{3} + O_{2}
     $$
   - This reaction is particularly useful in closed environments like space vehicles, where it is crucial to remove $CO_{2}$ exhaled by astronauts and simultaneously replenish the oxygen supply.
   - The ability of $Na_{2}O_{2}$ to perform both functions makes it an ideal choice for life support systems in space missions.

2. **Explanation for why other options are incorrect:**

- **Option 1 (NaOH):**
     - Sodium hydroxide (NaOH) can absorb $CO_{2}$ to form sodium carbonate (Na2CO3), but it does not release oxygen in the process. The reaction is:
       $$
       2NaOH + CO_{2} \rightarrow Na_{2}CO_{3} + H_{2}O
       $$
     - Since NaOH does not liberate oxygen, it is not suitable for the dual purpose required in space vehicles.

- **Option 2 ($Na_{2}O$):**
     - Sodium oxide ($Na_{2}O$) can react with $CO_{2}$ to form sodium carbonate, but similar to NaOH, it does not release oxygen. The reaction is:
       $$
       Na_{2}O + CO_{2} \rightarrow Na_{2}CO_{3}
       $$
     - Without the release of oxygen, $Na_{2}O$ cannot fulfill the requirement of both absorbing $CO_{2}$ and liberating $O_{2}$.

- **Option 4 (CaO):**
     - Calcium oxide (CaO), also known as quicklime, reacts with $CO_{2}$ to form calcium carbonate (CaCO3):
       $$
       CaO + CO_{2} \rightarrow CaCO_{3}
       $$
     - This reaction does not produce oxygen, making CaO unsuitable for the dual role needed in space vehicles.

In conclusion, $Na_{2}O_{2}$ is the only compound among the options that can both absorb carbon dioxide and release oxygen, making it the correct choice for use in space vehicles.