Consider following reactions:
`Ph-OHoverset("Na metal")rarr "Gas 'A'"`
`Ph-overset(O)overset(||)C-OHoverset(NaHCO_(3))rarr " Gas 'B'"`
The sum of molecular masses of gas A and B is ------- u.

Answer

To solve the problem, we need to analyze the two reactions provided and determine the molecular masses of the gases produced (Gas A and Gas B).

### Step 1: Identify Gas A from the first reaction
The first reaction is:
\[ \text{Ph-OH} \overset{\text{Na metal}}{\rightarrow} \text{Gas A} \]

Here, phenol (Ph-OH) reacts with sodium metal (Na). When sodium reacts with phenol, it typically leads to the formation of hydrogen gas (H₂) as a byproduct. The reaction can be represented as:
\[ \text{Ph-OH} + \text{Na} \rightarrow \text{Ph-O}^- \text{Na}^+ + \frac{1}{2} \text{H}_2 \]

Thus, Gas A is hydrogen (H₂).

**Molecular mass of Gas A (H₂):**
- The molecular mass of hydrogen (H) is approximately 1 u.
- Therefore, the molecular mass of H₂ = 2 × 1 = 2 u.

### Step 2: Identify Gas B from the second reaction
The second reaction is:
\[ \text{Ph-COOH} \overset{\text{NaHCO}_3}{\rightarrow} \text{Gas B} \]

In this case, benzoic acid (Ph-COOH) reacts with sodium bicarbonate (NaHCO₃). This reaction produces carbon dioxide (CO₂) gas as one of the products. The reaction can be represented as:
\[ \text{Ph-COOH} + \text{NaHCO}_3 \rightarrow \text{Ph-COO}^- \text{Na}^+ + \text{CO}_2 + \text{H}_2\text{O} \]

Thus, Gas B is carbon dioxide (CO₂).

**Molecular mass of Gas B (CO₂):**
- The molecular mass of carbon (C) is approximately 12 u, and that of oxygen (O) is approximately 16 u.
- Therefore, the molecular mass of CO₂ = 12 + 2 × 16 = 12 + 32 = 44 u.

### Step 3: Calculate the sum of the molecular masses of Gas A and Gas B
Now, we need to find the sum of the molecular masses of Gas A and Gas B:
\[ \text{Sum} = \text{Molecular mass of Gas A} + \text{Molecular mass of Gas B} \]
\[ \text{Sum} = 2 \, \text{u} + 44 \, \text{u} = 46 \, \text{u} \]

### Final Answer
The sum of the molecular masses of gas A and B is **46 u**.

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