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Question

Upon adding hydrochloric acid in copper oxide, it turns to blue-green color which is due to the formation of

This question was previously asked in
CDS 2 2026 Maths Question Paper (13-Sep-2026)
The correct answer is

Copper (II) chloride

Copper oxide (CuO) reacts with hydrochloric acid (HCl) to form copper(II) chloride and water: CuO + 2HCl → CuCl2 + H2O. The Cu2+ ion gives the solution its characteristic blue-green color, whereas copper(I) compounds are typically white or insoluble and would not produce this color.

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