Question 23

To balance the chemical equation \( \text{Na}_2\text{O} + \text{CaBr}_2 \rightarrow \text{NaBr} + \text{CaO} \), we need to ensure that the number of atoms of each element is the same on both sides.

1. **Identify the elements and their counts:**
- Reactants: \( \text{Na}_2\text{O} \) (2 Na, 1 O) and \( \text{CaBr}_2 \) (1 Ca, 2 Br)
- Products: \( \text{NaBr} \) (1 Na, 1 Br) and \( \text{CaO} \) (1 Ca, 1 O)

2. **Balancing the equation:**
- Start with Na: We have 2 Na on the left (from \( \text{Na}_2\text{O} \)), so we need 2 Na on the right:
- Place a coefficient of 2 in front of \( \text{NaBr} \):
\[
\text{Na}_2\text{O} + \text{CaBr}_2 \rightarrow 2 \text{NaBr} + \text{CaO}
\]
- Now, check the Br: We have 2 Br on the left (from \( \text{CaBr}_2 \)), and 2 on the right (from \( 2 \text{NaBr} \)).
- For Ca: There is 1 Ca on both sides (from \( \text{CaBr}_2 \) and \( \text{CaO} \)).
- O: We have 1 O on both sides (from \( \text{Na}_2\text{O} \) and \( \text{CaO} \)).

At this point, everything is balanced with the coefficients \( 1:1:2:1 \).

Therefore, the balanced equation is:
\[ 1 \text{Na}_2\text{O} + 1 \text{CaBr}_2 \rightarrow 2 \text{NaBr} + 1 \text{CaO} \]

Thus, the correct answer is:
**a. 1:1:2:1**