In Hatch and Slack pathway, the primary CO2 acceptor is
(1) Rubisco
(2) Oxaloacetic acid
(3) Phosphoglyceric acid
(4) Phosphoenol pyruvate

Option (4) Phosphoenol pyruvate is correct.

This is because – PEP (Phosphoenol pyruvate) is the primary CO2 acceptor in C4 or Hatch and Slack pathway.