The given matrix is:
```
4 6 2
1 5 -3
-7 0 9
```
The dimensions of the matrix are 3 x 3 because it has 3 rows and 3 columns.
The indicated element is "a23", which is not present in the matrix. The correct element in the 2nd row, 3rd column is 9.
Therefore, the correct answer is (b) 3x3; 9, a23.
Explanation:
- The matrix has 3 rows and 3 columns, so its dimensions are 3 x 3.
- The indicated element is a23, which does not exist in the matrix. However, the element in the 2nd row and 3rd column is 9.
- Therefore, the correct answer is (b) 3x3; 9, a23.