Why is freshly prepared ferrous sulphate solution used for testing the nitrate radical in the brown ring test?

Name an aqueous salt solution used for testing sulphate radical.

Iodine solution is used for testing the presence of

Why is a freshly prepared solution of FeSO_(4) used for the detection of nitrate and nitrite?

Ammonium molybdate is used to test the radical

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

Why is it necessary to prepare original solution for the detection of basic radicals?

When dilute ferrous sulphate solution is added lto an aqueous solution containing nitrate ion followed by careful addition of concentrated sulphuric acid along the sides of test tube a ,brown ring is formed at the iterface between the solution and sulphuric acid layers .Which is anion is confined by the appearance of brown ring .What the conposition of the brown ring ?

The brown compound formed in the ring test for nitrates contains the ion

Name the gas evolved when acidified iorn [II] sulphate reacts with dilute nitric acid in the brown ring test .

Why sodium carbonate extract is used for testing acid radicals?