The transition from isolated atomic orbitals to Bloch waves and energy bands, explaining why materials are conductors, semiconductors, or insulators.
The solution manual resources generally cover the following core areas. The difficulty level of the problems varies from basic definition checks to complex derivations.
An online search for "Ibach Luth solution manual" yields a complex picture. While you won't find a single, official PDF file, you will find a significant amount of related academic material: