There two radicals 口 and 囗 look very similar but they are not the same. The following is the difference between the radical 口 and the radical 囗.
Radical 口
口 denotes “mouth”. Characters with 口 relate to “mouth”, such as acts of mouth 吃, 喝; parts of mouth 嘴, 唇, etc. Check out more characters with the radical 口.
Radical 囗
囗 denotes “encircle”. Characters with 囗 relate to “encircle, surround, boundary, etc”, e.g. 围, 圈. Check out more characters with the radical 囗.
Tips on learning characters with 口 and 囗:
1. Most of the characters with 口 are formed in the semantic left-phonetic right structure.
2. Most of the characters in fully-enclosed structure with 囗 are formed in the phonetic inside-semantic outside structure.