Why a freshly prepared solution of `FeSO_4` is used in Lassaigne's test for nitrogen ?

Explanation

### Step-by-Step Solution:

1. **Understanding Lassaigne's Test**:
Lassaigne's test is a qualitative analysis technique used to detect the presence of nitrogen in organic compounds. The test involves fusing the organic compound with sodium to convert nitrogen into a soluble sodium salt.

2. **Role of Sodium**:
During the fusion process, sodium reacts with the organic compound containing nitrogen, leading to the formation of sodium cyanide (NaCN) among other products. This sodium cyanide is crucial for the subsequent reactions in the test.

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