If a matrix contain 5 rows and 3 columns, then the number of elements of the matrix is _____

Write a matrix which contains 1 row and 3 columns.

A matrix contains 2 rows and 4 columns and every element in the matrix is 1, then find the matrix.

A and B are two matrices such that A+B and AB are defined.If the number of rows of the matrix A is 5, then the number of columns of the matrix B is

If the number of rows and the number of columns of a matrix are equal and the matrix contains 25 elements, then the order of the matrix is _______

If the number of rows and that of columns of a matrix are equal and the matrix contains 16 elements, then the order of the matrix is _______