Question

Sometimes, the colour observed in Lassaigne’s test for nitrogen is green. It is because:

• A. of green colour of ferrous sulphate
• B. ferric ferrocyanide is also green
• C. of green colour of copper sulphate
• D. of excess of Fe³+ ions whose yellow colour makes the blue colour of ferric ferrocyanide appear green

Hint:

Observed colour in qualitative tests can be a result of: • More than one coloured species present • Colour mixing (blue + yellow = green)

Answer 1

The Correct Option is D

Step 1: In Lassaigne’s test for nitrogen, formation of ferric ferrocyanide gives a Prussian blue colour.
Step 2: If excess Fe³+ ions are present, they impart a yellow colour.
Step 3: The combination of blue (ferric ferrocyanide) and yellow (excess Fe³+) results in a green appearance.