**Category:** Inorganic Chemistry  
**Subtype:** Chemical Reactions  
**Problem Description:** This problem involves predicting the formation of precipitates from various chemical reactions. Specifically, it requires determining how many of the given experiments will produce a solid precipitate after the reactions are complete.

1. **Experiment 1:** Mixing \(\mathrm{NaHCO}_{3}\) with \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) at room temperature.
2. **Experiment 2:** Adding \(\mathrm{NaOH}\) to \(\mathrm{Ba}\left(\mathrm{HCO}_{3}\right)_{2}\).
3. **Experiment 3:** Reacting a mixture of copper (Cu) and \(\mathrm{Fe}_{3}\mathrm{O}_{4}\) with excess hydrochloric acid (HCl).
4. **Experiment 4:** Introducing \(1.2x\) moles of zinc (Zn) into a solution containing \(2.1x\) moles of \(\mathrm{FeCl}_{3}\).
5. **Experiment 5:** Adding \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) to excess \(\mathrm{AgNO}_{3}\).
6. **Experiment 6:** Adding excess \(\mathrm{Ba(OH)_{2}}\) to a solution of \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\).

**Objective:** Determine how many of these experiments result in the formation of a precipitate.  
**Answer Choices:** A. 3, B. 4, C. 2, D. 5.