Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| State (class) | Vacator | Reason for change | Successor | Date of successors formal installation |
| --- | --- | --- | --- | --- |
| Delaware (1) | George R. Riddle (D) | Died March 29, 1867 | James A. Bayard, Jr. (D) | April 5, 1867 |
| Arkansas (2) | Vacant | Arkansas re-admitted to the Union | Alexander McDonald (R) | June 22, 1868 |
| Arkansas (3) | Vacant | Arkansas re-admitted to the Union | Benjamin F. Rice (R) | June 23, 1868 |
| Florida (3) | Vacant | Florida re-admitted to the Union | Thomas W. Osborn (R) | June 25, 1868 |
| Louisiana (2) | Vacant | Louisiana re-admitted to the Union | John S. Harris (R) | July 8, 1868 |
| Louisiana (3) | Vacant | Louisiana re-admitted to the Union | William P. Kellogg (R) | July 9, 1868 |
| Alabama (2) | Vacant | Alabama re-admitted to the Union | Willard Warner (R) | July 13, 1868 |
| Alabama (3) | Vacant | Alabama re-admitted to the Union | George E. Spencer (R) | July 13, 1868 |
| Maryland (1) | Reverdy Johnson (D) | Resigned July 10, 1868 | William P. Whyte (D) | July 13, 1868 |
| North Carolina (2) | Vacant | North Carolina re-admitted to the Union | Joseph C. Abbott (R) | July 14, 1868 |
| North Carolina (3) | Vacant | North Carolina re-admitted to the Union | John Pool (R) | July 14, 1868 |
| South Carolina (2) | Vacant | South Carolina re-admitted to the Union | Thomas J. Robertson (R) | July 15, 1868 |
| South Carolina (3) | Vacant | South Carolina re-admitted to the Union | Frederick A. Sawyer (R) | July 16, 1868 |
Question:
List all state classes when successors were formally installed on June 22, 1868.
Answer:
Arkansas (2)