Question

Sodium nitroprusside added to an alkaline solution of sulphide ions produces a colouration which is:
A. Red
B. Blue
C. Brown
D. Purple

Answer 1

Hint: In chemistry, various elements react and form compounds. During a reaction, there are various states through the reaction which the compounds undergo. There is the production of intermediate ions products and released gases. These elements and products need not always be fully visible and detected by simple means. So for the detection of such elements, certain reactions are considered as the test for the element.

Complete step by step answer:
During the reaction, all the states and products are not necessarily visible and detected by simple means so certain reactions help us detect these hidden elements and products.
One of the tests which are used for the detection of sulphur is the Lassaigne'sṣ test. In this, the lassaigne’s extract is prepared which is the compound that helps for the testing in this test. Then two tests need to be performed through this extract namely the lead acetate test and sodium nitroprusside test
In the lead acetate test, a part of the extract is acidified with acetic acid, and then lead acetate is added, the formation of black precipitate proves the presence of sulphur. In the sodium nitroprusside test, sodium nitroprusside is added to a part of the extract. The appearance of purple colour confirms the presence of sulphur.

So, the correct answer is Option D.

Note: In this, a small piece of sodium is heated in a fusion tube till the formation of a shining state. After this, a small amount of the compound under detection is added to the tube and heated strongly. The red hot tube is taken into distilled water placed in a china dish. The contents are boiled for some time and filtered after cooling. This filtrate is called the sodium extract or the lassaigne’s extract.