Oil doesn't mix with water.
Those colors mixed.
I felt really sad and lonely because I couldn’t contribute to the conversation at all.
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means mix so the verb vocab version is to get mixed or to be mixed. This is when something is just getting mixed and you're not directly doing the action of mixing anything. You can remember this because the Tzar (ざる) of Russia is very impressed that things mix on their own and you're not doing the mixing.
The connotation for this word is you can't distinguish the things you're mixing, like combining paints, which become one mixed color that isn't two separate colors anymore.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: If you're not doing the mixing, in order for things to get mixed you call your ma (ま) up and ask her to mix it. What a terrible lazy child you are.