Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?

ANSER IN SIMPLE WORDS PLEASE

In test of halogens, the lassaigne solution is first treated (boiled) with dil HNO3 because the addition of this acid decomposes NaCN to HCN and Na2S to H2S to remove all the nitrogen and sulphur present in the solution so that only halogen would be available for testing.

The reactions carried are:

NaCN + HNO3 → NaNO3 + HCN

Na2S  + 2HNO3  → 2HNO3+ H2

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