One-to-one is used when you talk about transfer or communications. You may use one-to-one when you can identify a source and a destination. For eg., a one-to-one email is one sent from a single person to another, i.e., no ccs or bccs.

Understanding the Context

In maths, a one-to-one mapping maps one element of a set to a unique element in a target set. One-on-one is the correct adjective in your example. See Free ... The 'one hand' could be any generic hand (no article) or a specific one (definite article).

Key Insights

'The other' refers to the 'matching hand' of the first one. There can only ever be one, and it is being referred to explicitly as the partner of the first, therefore it needs a definite article. Which one is grammatically correct or better? I have two assignments, One of them is done. I have two assignments, One of which is done.

Final Thoughts

I watched a video tutorial that the teacher said the ... pronouns - "One of them" vs. "One of which" - English Language Learners ... 0 The phrase 'one of the' is used to describe something/someone from the same group. There are many birds on the tree. One of the birds is red.

This means we are talking about all the birds on the three but then when you want to be specific about the red bird, you use one of the. He is one of the soldiers who fights for their country - is correct. Is the use of "one of the" correct in the following context? "Which one is the best" is obviously a question format, so it makes sense that " which one the best is " should be the correct form.