Lassaigne's test is not used for the detection of which element?

When the Lassaigne's extract of a sulfur-containing compound is treated with sodium nitroprusside,what color is obtained?

Lassaigne's test is used for the detection of:

Lassaigne's test is not used for the detection of the element . . . . . . in the organic compound.

Given below are two statements:
Statement $I$ : Sulphanilic acid gives esterification test for carboxyl group.
Statement $II$ : Sulphanilic acid gives red colour in Lassaigne's test for extra element detection.
In the light of the above statements,choose the most appropriate answer from the options given below :

The violet color obtained in the Lassaigne's test for a sulfur-containing compound is due to the formation of which species?