Answer: B
E2 needs an axial leaving group and an axial anti hydrogen. In Q, Cl is already axial and H on C-2 and C-6 are both axial, so Saytzeff elimination toward the isopropyl-bearing carbon is possible and fast. In P, Cl must first flip to axial, which also flips isopropyl to axial; then C-2 carries no axial hydrogen and only the C-6 hydrogen is anti, giving the disubstituted alkene slowly.