`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 information provided and determine the type of amino acid based on the reaction and the amount of gas evolved.

### Step-by-Step Solution:

1. **Identify the Reaction**: The amino acid reacts with NaOH and CaO, which indicates a decarboxylation reaction. This reaction typically involves the removal of a carboxyl group (-COOH) from the amino acid, releasing carbon dioxide (CO2) gas.

2. **Determine the Gas Evolved**: In a decarboxylation reaction, for each carboxylic group present in the amino acid, one mole of CO2 is released.

3. **Analyze the Given Data**: The problem states that 0.1999 kg (or 199.9 grams) of salt is formed when the evolved gas is passed through lime water. The salt formed from CO2 reacting with lime water (calcium hydroxide) is calcium carbonate (CaCO3).

4. **Calculate Moles of Salt**: The molar mass of calcium carbonate (CaCO3) is approximately 100 grams/mole. To find the number of moles of CaCO3 formed:
\[ \text{Moles of CaCO3} = \frac{\text{mass of CaCO3}}{\text{molar mass of CaCO3}} = \frac{199.9 \text{ g}}{100 \text{ g/mol}} = 1.999 \text{ moles} \]
This can be approximated to 2 moles.

5. **Relate Moles of CO2 to Carboxylic Groups**: Since 1 mole of CO2 is released for each carboxylic group in the amino acid, and we have 2 moles of CO2, it indicates that there are 2 carboxylic groups present in the amino acid.

6. **Conclusion about the Amino Acid**: The amino acid must have 2 carboxylic groups and 1 amino group (NH2), which indicates that it is a dicarboxylic amino acid.

### Final Answer:
The amino acid has **two carboxylic groups**.