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 ... 0 The phrase 'one of the' is used to describe something/someone from the same group.

Key Insights

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. The 'one hand' could be any generic hand (no article) or a specific one (definite article).

Final Thoughts

'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. Both 'a single' and 'one single' are correct and commonly used phrases in English. They are interchangeable and can be used to emphasize the singularity of an item or person. 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. I watched a video tutorial that the teacher said the ... pronouns - "One of them" vs. "One of which" - English Language Learners ...