I brushed up on the use of Japanese commas (読点) here, but I don't think it explained this usage I found on 知恵袋.
The sentence is this:
忙しい、の対義語に当たる形容詞は何でしょうか。
Why exactly is the OP using the comma like this? The rule of thumb for me in English is that if you pause when speaking, you should use a comma in writing. I've just carried that over to Japanese somewhat, but this sentence would sound very unnatural to my (non-native) ears if one where to pause after 忙しい. Is that just not the case? Is this a standard use of the 読点 or internet slang, or...?
What is an adjective that is an antonym of "busy"?
. No idea if this is standard, though.