`alpha`-hydroxypropanoic acid can be prepared from ethanal by following the steps given in the sequence.

Options

A. Treat with HCN followed by acidic hydrolysis.
B. Treat with `NaHSO_(3)` followed by reaction with `Na_(2)CO_(3)`.
C. Treat with `H_(2)SO_(4)` followed by hydrolysis.
D. Treat with `K_(2)Cr_(2)O_(7)` in presence of suphuric acid.

Explanation

To prepare alpha-hydroxypropanoic acid from ethanal, we can follow these steps:

### Step 1: React Ethanal with HCN
- Ethanal (acetaldehyde) is treated with hydrogen cyanide (HCN). This reaction leads to the formation of a cyanohydrin. The reaction can be represented as follows:

\[ \text{CH}_3\text{CHO} + \text{HCN} \rightarrow \text{CH}_3\text{C(OH)(CN)}\text{H} \]

Here, the cyanide ion adds to the carbonyl carbon of ethanal, resulting in the formation of 2-hydroxypropanenitrile (cyanohydrin).

### Step 2: Hydrolysis of the Cyanohydrin
- The next step involves the hydrolysis of the cyanohydrin. This can be achieved by treating it with water in the presence of an acid (typically dilute sulfuric acid). The hydrolysis reaction can be represented as follows:

\[ \text{CH}_3\text{C(OH)(CN)}\text{H} + \text{H}_2\text{O} \xrightarrow{\text{H}^+} \text{CH}_3\text{C(OH)(COOH)}\text{H} \]

In this step, the nitrile group (-CN) is converted into a carboxylic acid (-COOH), resulting in the formation of alpha-hydroxypropanoic acid (lactic acid).

### Final Product
- The final product obtained from these reactions is alpha-hydroxypropanoic acid, which has the following structure:

\[ \text{CH}_3\text{C(OH)(COOH)}\text{H} \]

### Conclusion
- Therefore, the overall process involves the addition of HCN to ethanal followed by hydrolysis to yield alpha-hydroxypropanoic acid.

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