(i) `A+Na_(2)CO_(3) to B+C,`
(ii) `A overset(CO_(2))to` (Milkyl) C. ltbr. The chemical formula of A and B are respectively:

Options

A. NaOH and `Ca(OH)_(2)`
B. `Ca(OH)_(2) and NaOH`
C. `NaOH and CaO`
D. `CaO and Ca(OH)_(2)`

Explanation

To solve the problem step by step, we need to identify the compounds A and B from the given reactions.

### Step 1: Identify Compound A
The first reaction given is:
\[ A + \text{Na}_2\text{CO}_3 \rightarrow B + C \]

From the video transcript, we learn that the milky appearance is associated with calcium carbonate (CaCO₃). This suggests that A is likely to be a compound that can react with sodium carbonate (Na₂CO₃) to produce calcium carbonate.

### Step 2: Determine the Reaction
The likely candidate for compound A is calcium hydroxide (Ca(OH)₂). When calcium hydroxide reacts with sodium carbonate, it produces sodium hydroxide (NaOH) and calcium carbonate (CaCO₃).

The balanced reaction can be written as:
\[ \text{Ca(OH)}_2 + \text{Na}_2\text{CO}_3 \rightarrow 2 \text{NaOH} + \text{CaCO}_3 \]

Here, we can identify:
- B = NaOH (sodium hydroxide)
- C = CaCO₃ (calcium carbonate)

### Step 3: Identify the Second Reaction
The second part of the problem states:
\[ A \overset{\text{CO}_2}{\rightarrow} C \]

When calcium hydroxide (A) is treated with carbon dioxide (CO₂), it forms calcium carbonate (C):
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]

This confirms that the product formed is indeed calcium carbonate, which is known to produce a milky appearance when formed in a solution.

### Conclusion
From the analysis:
- Compound A is calcium hydroxide (Ca(OH)₂).
- Compound B is sodium hydroxide (NaOH).

Thus, the chemical formulas of A and B are respectively:
- A = Ca(OH)₂
- B = NaOH