A third portion of the unknown is made strongly basic with NaOH and heated. A gas is given off which turns red litmus blue. Indicate which ions were definitely present (+), definitely absent (-), or uncertain (?) _____Ba^2+ _____Ca^2+ _____ Sr^2+ _____Mg^2+ _____NH^+_4 _____K^+ _____Na^+ A combined group IV-V unknown was treated as follows: A. One portion, when treated with NH_3 and (NH_4)_2CO_3 and heated gives a precipitate A and solution B. The precipitate A is dissolved in acetic acid and ammonium acetate on addition of K_2CrO_4 to the solution it turns yellow but fails to give a precipitate. Treatment of this solution with NH_3 and alcohol gives no precipitate, but a white precipitate forms when (NH_4)_2C_2O_4 is then added. B. Solution B shows a violet flame which can be seen without the aid of a cobalt blue glass. Indicate which ions were definitely present (+), definitely absent (-), or uncertain (?). _____Ba^2+ _____Ca^2+ _____ Sr^2+ _____Mg^2+ _____NH^+_4 _____K^+ _____Na^+