The Steps in a Reaction Mechanism Are as Follows $\rightarrow$ Tl²⁺(aq) +Ag ⁺ (Aq)
Step 3: Tl^{2 +} (Aq)

The steps in a reaction mechanism are as follows.Which species is acting as a catalyst?
Step 1: Ag⁺(aq) +Ce⁴⁺(aq) ⇄ Ag²⁺(aq) +Ce³⁺(aq)
Step 2: Tl⁺(aq) + Ag²⁺(aq) $\rightarrow$ Tl²⁺(aq) +Ag ⁺ (aq)
Step 3: Tl^{2 +} (aq) + Ce⁴⁺(aq) $\rightarrow$ Tl³⁺(aq) + Ce ³⁺(aq)

A) Ag⁺
B) Tl⁺
C) Ce³⁺
D) Ag²⁺
E) Tl³⁺