Which preposition correctly completes the sentence: 'He writes ___ ink'?

Explanation

When referring to the substance used for writing, such as ink, the correct preposition is 'in.' For example, we say 'I write in ink.' However, when mentioning the tool, like a pencil, we use 'with' instead, as in 'I write with a pencil.' Therefore, the correct phrase is 'He writes in ink.'