Verifying molecular formulas of isomers

Steps:

• Examine structure of compound 1: count 4 C, 8 H, 2 O atoms.
• Examine structure of compound 2: count 4 C, 8 H, 2 O atoms.
• Examine structure of compound 3: count 4 C, 8 H, 2 O atoms.
• Confirm all match C4H8O2 formula.

Why D is correct:

• Molecular formula C4H8O2 requires exactly 4 carbon, 8 hydrogen, and 2 oxygen atoms, which all three compounds satisfy per standard organic notation.

Why the others are wrong:

• A omits compound 3, which has C4H8O2.
• B omits compound 2, which has C4H8O2.
• C omits compound 1, which has C4H8O2.

Final answer: D