None is always singular. None means “not one”. It is used in conjunction with “is”.
It is incorrect to use none with “are”.
Example – a) None of his injuries is life threatening. (correct)
b) None of his injuries are life threatening. (incorrect)
Correct use of the word “only”.
The word “only” refers to “one”. However it is not uncommon to find the word “only” misused.
Example – a) I only have 10 minutes to complete the task. (incorrect)
A close examination shows that the speaker or writer is saying that he or she is the only person who has 10 minutes to complete the task. What the person means to say is - I have only 10 minutes to complete the task. (correct)
Example – b) I only eat vegetables; I do not eat meat. (incorrect)
The person does not mean to imply that he or she is the only person in the world who eats vegetables and no meat.
I eat only vegetables; I do not eat meat. (correct)