4. Which of the following ions is classified as hard acid?(A) F⁻(B) Br⁻(C) Na⁺(D) Cs⁺(E) S²⁻

8. Which of the following statements about the complex ion [Co(en)₂Cl₂]⁺ is correct? (en = ethylenediamine)(A) It has two geometric isomers and two optical isomers.(B) Since en is a strong field ligand, the complex ion is paramagnetic.(C) It has cis and trans geometric isomers, but no optical isomers.(D) The geometric isomers of it have similar properties.(E) The oxidation state of Co is +1.