What happens to the ammonium cation (NH4+) when the pH is much lower than its pKa of about 9.3?

When the pH is much lower than the pKa of ammonium cation (NH₄⁺), it indicates an acidic environment. In this scenario, we can expect the ammonium cation to remain in its protonated form (NH₄⁺), as the pH is not high enough to favor the deprotonation process.

So, among the options provided:

• A: None of the molecules have a charge – This statement is incorrect because the ammonium ion (NH₄⁺) carries a positive charge.
• B: It is deprotonated and negatively charged – This statement is also incorrect since the low pH prevents the deprotonation of NH₄⁺. Instead, it stays as NH₄⁺ and does not become negatively charged.

In summary, at a pH much lower than the pKa, the ammonium cation exists predominantly in its charged form (NH₄⁺), and therefore, the correct answer is neither of the provided statements accurately describes the behavior of ammonium at these pH levels.