Answer:
It will turn red
Explanation:
Bases will turn the litmus paper (impregnated with an acid-base indicator) blue.
Acids will turn turn the litmus paper (impregnated with an acid-base indicator) red.
Since the produced HCl is a strong acid, the litmus paper will turn red, when touching the HCl.
The red shows the presence of an acid, in this case HCl.
Among the choices, the polyatomic ion is only the third choice, NH4+ where it is composed of nitrogen one atom of nitrogen and 4 atoms of hydrogen. Choice 2 is a monoatomic atom being composed only of calcium. Then, the first and fourth choices are not ions because they are not charged.
