When copper oxide is added to dilute hydrochloric acid, the colour of the acid changes to blue-green, due to the formation of _____.

Correct option is B

The correct answer is (b) copper (II) chloride.
Explanation: When copper oxide (CuO) is added to dilute hydrochloric acid (HCl), a chemical reaction takes place where copper oxide reacts with hydrochloric acid to form copper (II) chloride (CuCl₂) and water (H₂O).
The reaction can be written as:
CuO(s)+2HCl(aq)→CuCl₂(aq)+H₂O(l)
During this reaction:

• Copper (II) chloride (CuCl₂) is formed, which is a blue-green solution. This is why the color of the acid changes to blue-green.
  
• The water is formed as a byproduct, but it does not affect the color of the solution significantly.

Other Options:

• Copper (I) chloride (CuCl): Copper (I) chloride is typically white in color and is not formed in this reaction.
  
•  Hydrogen gas (H₂): This is not released in this particular reaction because copper oxide is not reacting in a way that releases hydrogen gas.

Thus, the correct answer is (b) copper (II) chloride.