Among the following cations, the number of cations which will give characteristic precipitate in their identification tests with \( \mathrm{K_4[Fe(CN)_6]} \) is ________.
\( \mathrm{Cu^{2+},\ Fe^{3+},\ Ba^{2+},\ Ca^{2+},\ NH_4^{+},\ Mg^{2+},\ Zn^{2+}} \)
