砂糖は湯に入れると溶ける。

sugar

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

hot water; hot bath; hot spring; molten iron

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

to put in; to let in; to take in; to bring in; to insert; to set (a jewel, etc.); to ink in (e.g. a tattoo); to admit; to accept; to employ; to hire; to accept; to comply; to grant; to adopt (a policy, etc.); to take (advice, etc.); to listen to; to pay attention to; to include; to pay (one's rent, etc.); to cast (a vote); to make (tea, coffee, etc.); to turn on (a switch, etc.); to send (a fax); to call

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

to melt; to thaw; to fuse; to dissolve