matrices – Can we say that this matrix is in row reduced echelon form?

Can we say that this matrix is in row reduced echelon form?
begin{bmatrix}1&0&0&3&1\0&0&1&0&0\0&0&0&0&1\0&0&0&0&0end{bmatrix}
I know that, it has leading numbers as 1 and other rows are zeros.
Is there a rule to have columns which have all zeros need to occur the beginning?
Your help is highly appreciated. Thank you.