If A and B are square matrix then (AB)T is 

Transpose of a Matrix:

The new matrix obtained by interchanging the rows and columns of the original matrix is called the transpose of the matrix.

It is denoted by A′or A^T

Properties of Transpose Matrix:

The transpose of a matrix is the matrix itself. ⇔ (A^T)^T = A

The transpose of matrix times a scalar (k) is equal to the constant times the transpose of the matrix. ⇔ (kA)^T = k A^T

The transpose of the sum or difference of two matrices is equivalent to the sum or difference of their transposes. ⇔ (A ± B)^T = A^T ± B^T

The transpose of the product of two matrices is equivalent to the product of their transposes in reversed order. ⇔ (AB) ^T = B^T A^T

The determinant of a square matrix is the same as the determinant of its transpose. ⇔ |A|  = |A^T|

From the above property statement 2 is the correct answer.