Which of the following pairs is expected to form colorless compounds?
(a) ⁵⁷La³⁺ and ⁶⁵Tb³⁺
(b) ⁵⁷La³⁺ and ⁷¹Lu³⁺
(c) ⁶⁰Nd³⁺ and ⁶¹Pm³⁺
(d) ⁶⁰Eu³⁺ and ⁶⁵Tb³⁺