Question

1. I read Chapter 2 of my history book.
2. I read chapter 2 of my history book.
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Which one is grammatical? Do we have to use the capital letter or not?

Answer 1

You'd have to look in the table of contents of the book or at the first page of the chapter.

If it's printed "Chapter 2" in the table of contents or on the first page of that chapter, then you use capital C.

If chapter 2 has an actual title, then that title would get the capital letters in the right places and you'd refer to it as chapter 2 or the second chapter.