Final answer:
Cementation is more effective when both porosity and permeability are high, as this allows for greater space for minerals to precipitate and better transport of fluids to cement particles together.
Step-by-step explanation:
Cementation happens more easily when porosity is high because there is more open space in the rock to hold and precipitate minerals.
However, for cementation to be effective, the connectivity of these pore spaces, which is a function of permeability, must also be high to allow fluids to transport the minerals that will cement the particles together. Rocks with high porosity and permeability, such as sandstones, are ideal for cementation because they have abundant spaces between grains and the pore spaces are well interconnected.
Therefore, the correct answers are (a) porosity is high and (b) permeability is high.