Which of the following element in +1 oxidation state has largest ionic radius?

Step-by-step solution

The ionic radius of alkali metals increases down the group. The number of occupied shells in Rb ⁺ (4 shells) is more than that in K ⁺ (3 shells), Na ⁺ (2 shells) and Li ⁺ (1 shell). Thus, it experiences smaller effective nuclear charge. Rb ⁺ has largest ionic radius than among other elements.