Choose the sequence that correctly orders the following ions according to magnitudes of their hydration energies.

a) Li⁺ < Na⁺ < K⁺ < Cs⁺
b) Cs⁺ < K⁺ < Na⁺ < Li⁺
c) Na⁺ < K⁺ < Cs⁺ < Li⁺
d) K⁺ < Na⁺ < Cs⁺ < Li⁺