Which method is not acceptable for cooling hot foods for refrigeration?

The not acceptable method is putting hot food in the refrigerator (or freezer).
This could raise the temperature in the fridge (upper than 6°C or 41°F), and so the other food contained in it.

Food should be put in the fridge in small pieces to cool faster.

As a tip, you should know that stainless steel cools food faster than plastic when it is on contact. And transfer heat also faster than plastic. Use it at your convenience if you want to heat (or cool) food faster.