C. setTimout(() => { formatName("John', 'Doe') }, 5000); It is the right answer. Time always given at the end

C is correct, remember the timeout value could be either a String or an Int value.
setTimeout(() => {formatName('John','Doe')}, "5000");

Explanation:
https://developer.mozilla.org/en-US/docs/Web/API/setTimeout#:~:text=If%20setTimeout()%20is%20called%20with%20delay%20value%20that%27s%20not%20a%20number%2C%20implicit%20type%20coercion%20is%20silently%20done%20on%20the%20value%20to%20convert%20it%20to%20a%20number

C is correct. B syntax is invalid -- the first argument must always be a function ref