The correct answer is option 3: "Where the foliations are moderately thin, the metamorphic rock tends to flake apart."

Option 1 states that some metamorphic rocks develop foliations due to the segregation of minerals into wavy bands or platy surfaces. This is correct. Foliation refers to the alignment of minerals in a rock and is a characteristic feature of many metamorphic rocks.

Option 2 states that when the foliations in a metamorphic rock develop into broad mineral bands, the rock becomes extremely hard. This is also correct. The alignment and compaction of minerals in a rock can make it stronger and more resistant to weathering and erosion.

Option 3, the incorrect statement, suggests that when the foliations in a metamorphic rock are moderately thin, the rock tends to flake apart. This is not true. While thin foliations may make a rock more susceptible to weathering and erosion, it does not necessarily mean it will flake apart.

Option 4 states that rocks that originally consisted of one dominant mineral can be foliated by metamorphism. This is correct. Metamorphism can cause the realignment of minerals and the development of foliation, even in rocks with a single mineral composition.