Writing it as H2O is really more correct. It isn't a number that should be written in words.
Ok, so it's like "o" or "oh" on the end rather than "ou."
How do you spell H2O?
That question doesn't make much sense.I wanted to ask how it is pronounced
In dialogue, I spell everything out. No one ever has spoken a number. We all speak words, not numbers. This is why every number and every letter has a proper spelling. Only vowels are spelled with their own letter.