Incorrect statement regarding the structure of dichromate is

Explanation:

The dichromate ion, ^2-Cr₂O₇, consists of two chromium atoms and seven oxygen atoms. In its structure, each chromium is surrounded by 4 oxygen atoms, not 3.

The chromium atoms are typically in an octahedral geometry, with four oxygen atoms forming bonds around each chromium atom. Therefore, option d is incorrect.

Correct interpretation of other options:

• Option a: Dichromate does indeed have two kinds of bond lengths. One is the Cr–O bond in the Cr–O–Cr linkage, and the other is the Cr=O bond in the terminal oxygen atoms.
• Option b: The Cr–O–Cr bond angle is approximately 126°, which is typical for such structures.
• Option c: There are indeed pπ–dπ bonds between Cr and O in the dichromate structure, as the chromium atoms can engage in d-orbital participation with the p-orbitals of oxygen.

Thus, the incorrect statement is option d.