"It" or "not it"?

English as a Second Language English Vocabulary, Grammar and Idioms
1

Correct or not correct? Same meaning or not same meaning?

a. This word is used with singular countable nouns to refer to one of a number of things or people, when it does not matter which one.
b. …people, when which one does not matter.

K

2

As far as I understand you want to insert the word that answers to all these requirements. What comes into my mind first is any but I’m not sure enough

3

Correct or not correct? Same meaning or not same meaning?

a. This word is used with singular countable nouns to refer to one of a number of things or people, when it does not matter which one.
b. This word is used with singular countable nouns to refer to one of a number of things or people, when which one does not matter.

K