星期二(xīng qī èr) - Tuesday in Mandarin

星期二 (xīngqī èr) is Tuesday: 星期 (xīngqī, "week") plus 二 (èr, "two"), the second day of the numbered run that starts at 星期一 (xīngqī yī, "Monday").

Like every weekday name, it drops straight in front of a verb with no preposition needed: 星期二我有中文课 (xīngqī èr wǒ yǒu Zhōngwén kè), "I have a Chinese class on Tuesday".

It can also sit at the end of a sentence as the answer to a question, or after a verb like 改到 (gǎi dào, "changed to") when a meeting or appointment moves, e.g. 会议改到星期二了 (huìyì gǎi dào xīngqī èr le), "the meeting has been moved to Tuesday".