Which of these matrices is in rowechelon form 1 0 0 2 1 0 3

Which of these matrices is in row-echelon form? [1 0 0 2 1 0 3 2 1] [0 1 0 1 0 1 0 1 0] [1 -1 6 0 1 2 0 0 1] [1 1 1 1 1 1 1 1 1]

Solution

Reduced echlon form of matrix is found by

in a matrix that all entries in a column below a leading coefficient ( the first nonzero number from the left, also called the pivot) are zeros.

Option B and Option C has all entries as zero below leading coefficient.