In the following sequence of reactions a compound A, (molecular formula C$$_6$$H$$_{12}$$O$$_2$$) with a straight chain structure gives a C$$_4$$ carboxylic acid. A is:
$$A \xrightarrow[\mathrm{H_3O^+}]{\mathrm{LiAlH_4}} B \xrightarrow{\text{Oxidation}} \text{C}_4\text{-carboxylic acid}$$

Compound $$\mathrm{A}$$ has molecular formula $$\mathrm{C_6H_{12}O_2}$$, corresponding to a saturated ester or carboxylic acid.

Reduction with $$\mathrm{LiAlH_4/H_3O^+}$$ converts an ester:

$$\mathrm{RCOOR' \rightarrow RCH_2OH + R'OH}$$

The resulting primary alcohols on oxidation form corresponding carboxylic acids.

Option $$\mathrm{C}$$ is:

$$\mathrm{CH_3CH_2CH_2COOCH_2CH_3}$$

which is ethyl butanoate.

Reduction produces:

$$\mathrm{1\text{-}Butanol\ (C_4)\ +\ Ethanol\ (C_2)}$$

Oxidation of $$\mathrm{1\text{-}Butanol}$$ gives:

$$\mathrm{Butanoic\ Acid\ (C_4)}$$

matching the condition given.

Option $$\mathrm{D}$$ produces only $$\mathrm{C_3}$$ alcohols and hence forms $$\mathrm{C_3}$$ carboxylic acid on oxidation.

Therefore, the correct compound is:

$$\mathrm{CH_3CH_2CH_2COOCH_2CH_3}$$

Correct Option: $$\mathrm{C}$$