In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

[EX Q]: Most smokers try to quit at least _ or six times before they succeed, researchers say.
[EX A]: five

[EX Q]: Copper has _ stable isotopes.
[EX A]: two

[EX Q]: Salts are known in the _ oxidation states.
[EX A]:
three