An aqueous solution of a salt X turns blood red on treatment with SCN⁻ and blue on treatment with K₄[Fe(CN)₆]. X also gives a positive chromyl chloride test. The salt X is:

The salt X is ferric chloride FeCl₃.
It reacts with SCN⁻ to form blood red ferric thiocyanate.
FeCl₃ + 3SCN⁻ → Fe(SCN)₃ + 3Cl⁻
It also reacts with potassium ferrocyanide to form blue colored ferric ferrocyanide.
4FeCl₃ + 3K₄[Fe(CN)₆] → Fe₄[Fe(CN)₆]₃ + 12KCl
Also, since, salt X contains chlorine, it gives positive chromyl chloride test.
4Cl⁻ + K₂Cr₂O₇ + 3H₂SO₄ → K₂SO₄ + 2SO₂ + 2CrO₂Cl₂↑ + 3H₂O
In this test, orange yellow chromyl chloride gas is obtained.