The question describes an organic compound that:

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Question 11:
The question describes an organic compound that:

• "Evolve steamy white fumes with $\text{PCl}_5$" - This indicates the presence of a hydroxyl (-OH) group, characteristic of alcohols or carboxylic acids. The reaction produces $\text{HCl}$ gas, which forms steamy white fumes.
• "Equally evolve a colourless gas with sodium carbonate" - This indicates the presence of a carboxylic acid (-COOH) group, as carboxylic acids react with carbonates to produce carbon dioxide ($\text{CO}_2$) gas, which is colourless. Alcohols do not react with sodium carbonate.

Combining these two observations, the compound must be a carboxylic acid.
Let's examine the options:

• A. $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ (Propan-1-ol) is an alcohol. It reacts with $\text{PCl}_5$ but not with sodium carbonate.
• B. $\text{CH}_3\text{CH}=\text{CH(OH)}$ (Propen-1-ol) is an enol, which is generally unstable. It has an -OH group but is not a carboxylic acid.
• C. $\text{CH}_3\text{CH}_2\text{CH}_2\text{Cl}$ (1-Chloropropane) is a haloalkane. It does not have an -OH group and does not react with sodium carbonate to produce gas.
• D. $\text{CH}_3\text{CH}_2\text{COOH}$ (Propanoic acid) is a carboxylic acid. It contains an -OH group (within the -COOH) that reacts with $\text{PCl}_5$ and a -COOH group that reacts with sodium carbonate to produce $\text{CO}_2$.

The final answer is $\boxed{\text{D}}$.