其中【qízhōng】

其中 means "among them" or "in it", and always points back to a group or a whole that has just been named. It usually opens the second clause, and what follows picks out a part of that group.

其中之一

X 是其中之一 means "X is one of them". The group comes first, and 其中之一 closes the sentence.

在其中

After a verb or with 在, 其中 means "in it": inside the activity or place already mentioned.

Mistakes

其中 stands for the group, so it can't follow a noun the way English "among" does. After a noun, use 中 or 里.

• × 在我的朋友其中，他最高 → 在我的朋友中，他最高
• × 其中我们班，有三个人会说中文 → 我们班有三个人会说中文

If no group has been named yet, 其中 has nothing to point back to.