49. 12-Crown-4 binds with the alkali metal ions in the following order: Li⁺＞＞ Na⁺＞ K⁺＞ Cs⁺. It is due to the (A) Right size of cation (B) Conformational flexibility of crown ether (C) Hydrophobicity of crown ether (D) Change in entropy being positive

4. Both ZnS and CaF₂ have a face-centered cubic unit cell where the S²⁻ and Ca²⁺ ions are closest packed in each structure. Which of the following is true? (A) There are 4 tetrahedral holes empty in each structure. (B) In both compounds, one-half of the tetrahedral holes are filled. (C) In both compounds, all the tetrahedral holes are filled. (D) There are 8 Zn²⁺ ions and 4 F⁻ ions in the unit cell. (E) In ZnS, one-half of the tetrahedral holes are filled by Zn²⁺ ions, whereas in CaF₂ all the tetrahedral holes are filled with F⁻ ions.

49. 12-Crown-4 binds with the alkali metal ions in the following order: Li⁺＞＞ Na⁺＞ K⁺＞ Cs⁺. It is due to the
(A) Right size of cation
(B) Conformational flexibility of crown ether
(C) Hydrophobicity of crown ether
(D) Change in entropy being positive

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