Correct option is A
Explanation-
"C2′" refers to the second carbon on the ribose ring. "Endo" means that this carbon is on the same side as the base (i.e., above the ring plane). If C2′ is above the plane, it is called C2′-endo.
So, the correct answer is option A : C2′-endo
Incorrect options-
Option 2: C2′-exo
Would require C2′ to be below the ring plane, which is not seen here.
Option 3: C3′-endo
Would require C3′ to be above the ring plane, which it isn't in this image.
Option 4: C5′-exo
C5′ is not a part of the ring pucker—it is part of the side chain and not used in pucker classification.
