18. Which one of the following is classified as a soft acid? (A) Ca²⁺ (B) Cl⁻ (C) Co³⁺ (D) Cr⁶⁺ (E) Cu⁺

6. Which one of the following functions is the wave function of a sp hybridized orbital of an atom? (A) (1/2)1/2(ψ(s) + ψ(p)) (B) (1/3)1/2ψ(s) - (1/6)1/2ψ(px) + (1/2)1/2ψ(py) (C) (1/3)1/2ψ(s) - (1/6)1/2ψ(px) - (1/2)1/2ψ(py) (D) (1/2)(ψ(s) + ψ(px) + ψ(py) + ψ(pz)) (E) (1/2)(ψ(s) + ψ(px) - ψ(py) - ψ(pz))