The correct option is C It is too informal
Option C: It is too informal
The lines "This will be helpful for you buddy, so do come. I will wait for you." are in an informal tone, as the words 'buddy' and 'I will wait for you' are not used in formal and public notices. Hence C is the correct option.
Option A: The notice is grammatically sound. Only the tone of the content is informal. Hence A is incorrect.
Option B: The notice is not formal. On the contrary, the notice is supposed to be too formal. Hence B is incorrect.
Option D is incorrect because the answer lies in C.