Question

Does entropy increase when heat flow from cold to hot

Answer 1

Nope it doesn't.

See entropy is a weird concept. It is easy to understand if you pay attention, but it is also one of the most misunderstood concept.

But as a rule, ENTROPY always INCREASES if the process is SPONTANEOUS.

Spontaneous means happens by itself, without any help.

But do you often see a cold body giving heat to hot body by itself?

Refrigerator if an example where it happens you might say, BUT NO! They do it with the help of external sources (electricity!).

So if a process is non spontaneous, then Entropy must decrease.

If you want to know more, comment. You can watch khanacademy's videos on entropy. They are super helpful.