Ions with a single electron such as He⁺, Li²⁺, and Be³⁺ are described by the H atom wave functions with Z/a₀ substituted for 1/a₀, where Z is the nuclear charge. The 1s wave function becomes ψ (r) = 1/√π (Z/a₀)^3/2. Using this result, compare the mean value of the radius r at which you would find the 1s electron in H, He⁺, Li²⁺, and Be³⁺ ?