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.

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

Here, phenol (Ph-OH) reacts with sodium metal (Na). The reaction produces sodium phenoxide and hydrogen gas (H₂).

### Step 2: Determine the gas A
From the first reaction, we can conclude that:
- The gas produced (Gas A) is hydrogen (H₂).
- The molecular mass of hydrogen (H₂) is calculated as follows:
\[ \text{Molecular mass of H₂} = 2 \times 1 = 2 \text{ u} \]

### Step 3: Identify the second reaction
The second reaction is:
\[ \text{Ph-COOH} + \text{NaHCO}_3 \rightarrow \text{Gas B} \]

In this reaction, benzoic acid (Ph-COOH) reacts with sodium bicarbonate (NaHCO₃). This is an acid-base reaction that produces sodium benzoate, water, and carbon dioxide (CO₂).

### Step 4: Determine the gas B
From the second reaction, we can conclude that:
- The gas produced (Gas B) is carbon dioxide (CO₂).
- The molecular mass of carbon dioxide (CO₂) is calculated as follows:
\[ \text{Molecular mass of CO₂} = 12 \text{ (C)} + 2 \times 16 \text{ (O)} = 12 + 32 = 44 \text{ u} \]

### Step 5: Calculate the sum of the molecular masses
Now, we will add the molecular masses of gas A and gas B:
\[ \text{Sum of molecular masses} = \text{Molecular mass of H₂} + \text{Molecular mass of CO₂} = 2 \text{ u} + 44 \text{ u} = 46 \text{ u} \]

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

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