Undecidable Problems Practice Test

In a passage about software verification, undecidable problems were described as having no algorithm that always halted with a correct decision; the Halting Problem asked whether a program stopped; this blocked perfect analyzers; NP-complete problems were different because they remained decidable though sometimes slow. What makes undecidable problems distinct from NP-complete problems according to the text?

In a verification-focused passage, undecidable problems were defined as having no algorithm that always halted with correct answers; the Halting Problem asked whether code stopped; this blocked perfect bug-finding; NP-complete problems differed because they stayed decidable though potentially slow. What makes undecidable problems distinct from NP-complete problems according to the text?