Which one of the following is an example of Hormone releasing IUD ?

The correct answer is LNG 20.

To understand why LNG 20 is the correct option, let us look at the classification of Intrauterine Devices (IUDs):

1. Non-medicated IUDs: These devices do not release any chemical substances or hormones. An example is Lippes Loop.
2. Copper-releasing IUDs: These devices release copper ions (${\mathrm{Cu}}^{2+}$), which suppress sperm motility and the fertilizing capacity of sperms. Examples include CuT, Cu7, and Multiload 375.
3. Hormone-releasing IUDs: These devices release hormones (such as levonorgestrel or progesterone) that make the uterus unsuitable for implantation and the cervix hostile to the sperms. Examples include Progestasert and LNG-20 (Levonorgestrel-20).

Therefore, among the given options, LNG 20 is a hormone-releasing IUD, while CuT, Cu 7, and Multiload 375 are copper-releasing IUDs.