When alcohol oxidizes, it becomes aldehyde, but what happens when aldehyde oxidizes?
Literal
Alcohol [subj-が] oxidize-[conditional-と] aldehyde become [but-が], aldehyde [subj-が] oxidize-[conditional-と] how become [question-ますか].
アルコール, アルデヒド — chemistry loanwords. 酸化する 'to oxidize' (酸化 'oxidation' + する). The conditional と is used for natural/scientific consequences. ~とどうなりますか 'what happens when X?' is a standard science question format. A chemistry textbook question.