Here's why:

* Ammonium ion (NH₄⁺): This is a positively charged ion.

* Carbide ion (C₄⁻⁴): This is a hypothetical ion with a very high negative charge.

The large difference in charge between these two ions would make it extremely difficult for them to form a stable ionic bond.

Instead of forming ammonium carbide, ammonium ions would likely react with water or other substances in the environment.