The correct Active/Passive form of the given sentence is:

☀ Grammar is studied by some students on the internet.

 Explanation for other options:

☀ Grammar is being studying by many students on the internet. This option is in the passive voice, but the verb form is incorrect. The correct form should be "Grammar is being studied by many students on the internet."

☀ Grammar have been studying by many students on the internet. This option uses the wrong verb form. The subject "Grammar" requires the singular form of the verb "has been studied" instead of "have been studying."

☀ Grammar is studying by many students on the internet. This option is in the active voice and changes the meaning of the sentence. In this form, "Grammar" becomes the subject performing the action, which implies that grammar itself is studying something, which is not the intended meaning.