If both N and S are present in an organic compound, . . . . . . . . . colouration is obtained in Lassaigne's test.

Explanation

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**: Lassaigne's test is a qualitative analysis method used to detect the presence of certain elements in organic compounds, particularly nitrogen (N) and sulfur (S).

2. **Presence of Nitrogen and Sulfur**: When both nitrogen and sulfur are present in an organic compound, they can react with sodium during the fusion process to form sodium thiocyanate (NaSCN).

3. **Formation of Sodium Thiocyanate**: The reaction can be summarized as:
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