Explanation:

Lassaigne's test is a qualitative test for the presence of nitrogen and sulfur in an organic compound. The test involves the conversion of these elements into their sodium salts, which can then be detected by various chemical tests.

Sodium extract preparation involves the following steps:

Step 1: Heating the organic compound with metallic sodium

The organic compound is heated with metallic sodium in a hard glass test tube. The sodium reacts with the organic compound to form sodium salts of the various elements present in the compound.

Step 2: Extraction of the sodium salts

The mixture of the organic compound and sodium is then extracted with water. The water extracts the sodium salts of the various elements present in the compound.

Step 3: Testing for the presence of nitrogen and sulfur

The sodium extract is then tested for the presence of nitrogen and sulfur using various chemical tests.

The reaction of nitrogen and sulfur with metallic sodium can be represented as follows:

N + Na → NaCN
S + Na → Na2S

This means that nitrogen and sulfur in the organic compound are converted into sodium cyanide (NaCN) and sodium sulfide (Na2S) respectively during the Lassaigne's test.

However, both of these compounds are highly toxic and can be hazardous to handle. To avoid this, an alternative method is used, where nitrogen and sulfur are converted into sodium thiocyanate (NaSCN) instead of NaCN and Na2S.

The reaction of nitrogen and sulfur with sodium in the presence of carbon produces sodium thiocyanate:

N + Na + C → NaCN
S + Na + C → Na2S
2NaCN + S → Na2S + C + N2
2NaSCN + C → Na2S + N2 + CO

Therefore, the correct answer is option 'C' - NaSCN.