When talking about recycling, people increasingly mention the popular trend of recycling old clothes to make new outfits.
In this sentence, there are two separate phrases: "When talking about recycling" and "people increasingly mention the popular trend of recycling old clothes to make new outfits." These phrases can be separated by commas to make the sentence clearer and easier to read.
The first comma is placed after "recycling" to indicate the end of the introductory phrase "When talking about recycling." The second comma is placed after "clothes" to separate the main clause "people increasingly mention the popular trend of recycling old clothes to make new outfits" from the dependent clause "to make new outfits."
Therefore, the commas should be placed as follows: "When talking about recycling, people increasingly mention the popular trend of recycling old clothes to make new outfits."