Which of the following is not a form of shirk according to the Qur'an?

Monotheism is not a form of shirk according to the Qur'an. Shirk refers to the sin of associating partners with Allah or believing in multiple gods. The Qur'an teaches the belief in the Oneness of Allah (Tawheed) and monotheism is the foundation of Islamic belief. Monotheism is the belief in the existence of one God without any partners or associates. The other options mentioned are all considered forms of shirk in Islam: atheism denies the existence of Allah, trinity attributes partners to Allah, and polytheism believes in multiple gods.