The incorrect sentence is: "None of the material is missing."
This is because "none" can be considered a plural pronoun, especially in more formal or traditional grammar. A more grammatically correct version would be: "None of the materials are missing." However, in modern usage, "none" can function as a singular pronoun as well, so the original sentence may not be universally considered incorrect depending on the context.
If looking for a clear incorrectness, it would depend on the context of the materials being referred to (countable vs uncountable).
Let me know if you need further clarification!