Throw this pen . . . . . . . . the dustbin.

In this sentence, "Throw this pen into the dustbin," the preposition "into" is the correct choice. It indicates the direction of the action, specifying that you should throw the pen in the direction of the dustbin, with the intention of it landing inside the dustbin.

The other options are not suitable for this context:

Option B: "in" would imply that you should throw the pen while it is already inside the dustbin, which is not the intended meaning.
Option C: "none" is not correct as a preposition is needed in the sentence.
Option D: "on" would imply that you should throw the pen on top of the dustbin, which is also not the intended meaning.