Which of the following pairs of ions would be expected to form a precipitate when dilute solutions are mixed?
(a) \(\mathrm{NH}_4{ }^+,\left[\mathrm{Co}\left(\mathrm{NO}_2\right)_6\right]^{3-}\)
(b) \(\mathrm{NH}_4{ }^{+}, \mathrm{CO}_3{ }^{2-} \)
(c) \(\mathrm{Fe}^{3 +}, \mathrm{OH}^{-} \)
(d) \(\mathrm{Ba}^{2+}, \mathrm{SO}_4^{2-}\)
1. (a), (b),(c)
2. (a), (c), (d)
3. (a), (b)
4. None of the above