Which requires more energy: turning one mole of ice into water, or turning one mole of water into steam?
Literal
1 mole [possessive-の] ice [object-を] water [locative-に] make-[time-とき] [and-と], 1 mole [possessive-の] water [object-を] steam [locative-に] make-[time-とき], more more energy [subject-が] necessary is [nominalized-の] [topic-は]?
A classic physics/chemistry exam question about phase transitions (the answer is vaporization, which requires far more energy than melting). The structure is a comparison: A にするときと B にするとき、より多くの X が必要 — 'between doing A and doing B, which requires more X?'. The verb-nominalized clause ending in の serves as the topic of the question. より多くの... ('more ~') is the comparative pattern for formal contexts.