An unknown blue liquid was boiled. a blue solid was left after the liquid boiled away. is the unknown material a mixture or a pure substance?

i think the unknown liquid is a

hello! if you would like i could share a research essay i did a month or two ago!

plato users

given bodies of water

pacific / arctic / indian / southern

[ a ] the caribbean sea

[ b ] the northern ocean

[ c ] the atlantic ocean

[ d ] the barents sea

with this being the given answers