A question about ammonium chloride?

The classic method of preparing ammonia on a laboratory scale is the react an ammonium salt ( such as ammonium chloride) with a base (such as sodium hydroxide).
NH4Cl + NaOH → NaCl + NH3 + H2O
This reaction fulfils a requirement of a metathesis reaction, because a gas (NH3) is formed.
If you mix any of the other choices, no metathesis reaction occurs and you merely have a mixture of the different ions as in solution.

NH4Cl + HNO3 ↔ NH4+ + Cl- + H+ + NO3-
NH4Cl + HCl ↔ NH4+ + H+ + Cl-
MgSO4 + NH4Cl ↔ NH4+ + Cl- + Mg 2+ + SO4 2-
The above are not reactions.

Acids can be defined as having the ability to donate protons.
Bases can be defined as having the ability to collect protons.
Amm chloride, NH4Cl has a positive NH4+ ion.
the base, sodium hydroxide, NaOH, collects a proton (hydrogen atom with no electrons) from Ammonium ion, to leave benind ammonia, NH3. In collecting a proton, NaOH forms water, H2O and NaCl(aq) is left over.
The overall equation is
NH4Cl(aq) + NaOH(aq) --> NaCl(aq) + NH3(aq) + H2O(l)