Question:

Appearance of blood red colour on treatment of the sodium fusion extract of an organic compound with FeSO₄ in presence of concentrated H₂SO₄ indicates the presence of element(s).

Updated On: Jan 13, 2026

N & S
Br
S
N

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The Correct Option is A

Approach Solution - 1

To determine which elements are present in the organic compound based on the appearance of a blood red color, let's consider the chemistry involved in the test mentioned.

When an organic compound containing nitrogen and sulfur is subjected to sodium fusion, elements like nitrogen, sulfur, and halogens form ionic compounds with sodium. For nitrogen-containing compounds, sodium reacts to form sodium cyanide (NaCN).
The subsequent reaction with ferrous sulfate (FeSO₄) is known as the Lassaigne's test, specifically for detecting nitrogen as part of a (NaCN) complex:
The complex formation involves the following reactions:
- Sodium cyanide (NaCN) forms Fe²⁺Cyanide complex:
- The equations can be represented as: \(6NaCN + FeSO\_4 \rightarrow Na\_4[Fe(CN)\_6] + Na\_2SO\_4\)
- The formed Na₄[Fe(CN)₆] reacts with ferric ions (formed in situ by the oxidation of Fe²⁺ by concentrated H₂SO₄), resulting in: \(3Na\_4[Fe(CN)\_6] + 4Fe^{3+} + 12H^+ \rightarrow Fe_4[Fe(CN)\_6]_3 + 12Na^+ + 6H_2O\)
- This forms a Prussian blue color if nitrogen is present alone but a blood red color if sulfur is present along with nitrogen because of the formation of ferric thiocyanate (Fe(SCN)₃).
Therefore, the presence of both nitrogen and sulfur is needed to form the characteristic blood red color due to ferric thiocyanate.

This leads us to conclude that the appearance of a blood red color confirms the presence of both nitrogen and sulfur in the original organic compound.

Correct Answer: N & S

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Approach Solution -2

The appearance of a blood red color upon this reaction indicates the presence of both nitrogen and sulphur in the compound, as they combine to form thiocyanate ions (SCN⁻), which react with Fe³⁺ to produce Fe(SCN)₃ with the characteristic blood red color.

So, the correct answer is : N & S.

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Concepts Used:

Classification of Organic Compounds

Organic Compounds can be classified into:

Classification based on the structure:

The classification of organic compounds is based on structure such as:

Acyclic or open chain compounds - Acyclic compounds are just opposite to cyclic compounds because their molecules don’t form any ring. It is called open-chain compounds because they have a linear structure.
Cyclic or closed chain compounds - Cyclic compounds are also known as “Ring compounds.”

Appearance of blood red colour on treatment of the sodium fusion extract of an organic compound with FeSO4 in presence of concentrated H2SO4 indicates the presence of element(s).