The first is right and the second is wrong. You usually need an object for "tell" e,g, it

'I'll tell to my mother' is NOT correct. We would never say that. 'I'll tell it to my mother' is OK, but only if you know what 'it' is. For example, if someone tells you a joke, you might say 'That's a funny joke. I'll tell it to my mother.' In fact, in most situations, we would simply say 'I'll tell my mother', with no 'it' and no 'to'. For example: 'There's a new ice cream shop in town' 'Is there? I'll tell my mother.'

"Теll" is a transitive not complex transitive verb. Complex transitive verbs require both an indirect and a direct object, while transitive require only one object. "I'll tell my mother" is correct. "My mother" is the direct object.

Hello Mirco The verb pattern should be 'tell sth to sb' or 'tell sb sth', so the correct version is 'tell it to my mother'. The only other possibility is 'tell my mother', when you already have a context. Hope this helps

Mirco - there is no difference of opinion here. In your question, you wrote the second option as "tell to my mother" which we all agree is wrong. In your recent comment, you gave another option of "tell my mother" (no "to") which I agree is good - and I am sure the other teachers would agree with me.