Three textbook facts on factorials, orthogonal contrasts and confounding

Consider the statements: (1) If the presence of interaction inflates the error mean square, one should use factorial designs. (2) Two contrasts with coefficients $\{c_i\}$ and $\{d_i\}$ are orthogonal if $\sum_{i=1}^ac_id_i=0$. (3) Confounding is a design technique for arranging a complete factorial experiment in blocks. Which of the above statements are correct?