A beaker initially contains an aqueous solution of Zn(NO3)2. Sodium hydroxide is added dropwise until excess OH⁻ is present, producing a precipitate that subsequently dissolves to form [Zn(OH)4]2−. Concentrated hydrochloric acid is then added, regenerating Zn2+ in solution.
Which of the following ions remains a spectator throughout the entire sequence?
a) Cl−
b) Na+
c) Zn2+
d) OH−