Chemistry - Complete d-block Question with Solution | TestHub

Identification of Ore (A): The ore is chromite (FeCr₂O₄), which is a combination of basic FeO and amphoteric Cr₂O₃, making option (C) correct.

Reaction Flow: Roasting with Na₂CO₃ (B) gives yellow Na₂CrO₄ (C), residue Fe₂O₃ (D), and acidic CO₂ gas (E), which does not decolorize KMnO₄ (making D incorrect).

Conversion to Dichromate: Adding H₂SO₄ converts the yellow chromate (C) into orange-red sodium dichromate, Na₂Cr₂O₇ (F).

Crystallization & Standard: Na₂Cr₂O₇ is hygroscopic and cannot be a primary standard (making B incorrect); adding KCl yields K₂Cr₂O₇ (G) because NaCl crystallizes out much faster from the hot concentrated solution, making option (A) correct.