JAMB - Chemistry (2006 - No. 11)

The sulphide that is generally considered insoluble in dilute hydrochloric acid is copper sulphide (CuS). 

While many metal sulphides dissolve in dilute HCl, copper sulphide is one of the few that remains undissolved due to its relatively low solubility product. 

When CuS is added to dilute HCl, no visible reaction occurs, indicating its insolubility. In order to dissolve copper sulphide, a stronger acid like nitric acid (HNO3) is typically required.