`underset("(1 mole)")("Amino acid")underset(Delta)overset(NaOH+CaO)(to)` gas evolved
`underset("Lime water")overset("Pass in")(to)underset(0.1999 kg)("salt")`
Amino acid having

Options

A. Two `NH_2` groups
B. One - COOH group
C. Two - COOH groups
D. Three - COOH groups

Answer

To solve the problem, we need to analyze the reaction of an amino acid with NaOH and CaO, and the subsequent reaction of the evolved gas with lime water. Here’s a step-by-step breakdown:

### Step 1: Understand the Reaction
When 1 mole of an amino acid reacts with NaOH and CaO, a gas is evolved. The gas evolved in this reaction is carbon dioxide (CO2), which is produced during the decarboxylation of the amino acid.

**Hint:** Identify the type of reaction taking place when an amino acid is treated with a strong base like NaOH.

### Step 2: Decarboxylation of Amino Acid
In the presence of NaOH, the carboxylic acid group (-COOH) of the amino acid undergoes decarboxylation, releasing CO2. The general reaction can be represented as:
\[ \text{RCH}_2\text{COOH} + \text{NaOH} \rightarrow \text{RCH}_2 + \text{CO}_2 + \text{H}_2\text{O} \]

**Hint:** Recall that decarboxylation leads to the loss of a carboxyl group as CO2.

### Step 3: Determine the Amount of CO2 Evolved
The amount of CO2 evolved is directly related to the number of carboxylic acid groups present in the amino acid. If there are 'n' carboxylic groups, then 'n' moles of CO2 will be produced.

**Hint:** Consider how the number of carboxylic groups affects the amount of CO2 produced.

### Step 4: Reaction with Lime Water
The CO2 gas evolved is then passed through lime water (Ca(OH)2). The reaction that occurs is:
\[ \text{CO}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]
This results in the formation of calcium carbonate (CaCO3).

**Hint:** Understand the significance of lime water in detecting CO2.

### Step 5: Calculate the Mass of Salt Formed
According to the problem, 0.1999 kg (or 199.9 g) of salt is formed. The molar mass of calcium carbonate (CaCO3) is approximately 100 g/mol.

To find the number of moles of CaCO3 formed:
\[ \text{Moles of CaCO}_3 = \frac{199.9 \text{ g}}{100 \text{ g/mol}} = 1.999 \text{ moles} \approx 2 \text{ moles} \]

**Hint:** Use the molar mass to convert grams to moles.

### Step 6: Relate Moles of CO2 to Carboxylic Groups
Since each mole of CO2 corresponds to one carboxylic acid group, the formation of 2 moles of CO2 indicates that the amino acid has 2 carboxylic acid groups.

**Hint:** Connect the amount of CO2 evolved to the number of carboxylic groups in the amino acid.

### Conclusion
The amino acid in question has 2 carboxylic acid groups (COOH). Therefore, the correct answer is that the amino acid consists of 2 COOH groups.

**Final Answer:** The amino acid has 2 COOH groups.