ゼリーは冷えると固くなる。

jello; gelatin dessert; jelly; gel; jelly

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to grow cold (from room temperature, e.g. in refrigerator); to get chilly; to cool down

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

hard; solid; tough; stiff; tight; wooden; unpolished (e.g. writing); strong; firm (not viscous or easily moved); safe; steady; honest; steadfast; obstinate; stubborn; bookish; formal; stuffy

to become; to get; to grow; to be; to reach; to attain; to result in; to prove to be; to consist of; to be composed of; to succeed; to be complete; to change into; to be exchanged for; to play a role; to be promoted; to do ...