In Excel, how are columns labeled?

Using alpha characters from left to right

The correct answer is option 2- Using alpha characters from left to right.

Rows are numbered numerically from top to bottom while Columns are referred by alpha characters from left to right. In Excel 2007, there are 65536 Rows which are numbered as 1, 2, 3, … 65,536. These numbers are shown on the left most portion of the worksheet. Columns (total 256 in Excel) are identified by letters, such as A, B, C,.. AA… IV, and are shown on the horizontal box just above Row 1.