Give the correct order of initials T (true) or F (false) for following statements: I. In an anti-flu β Solid State Chemistry Question
Question
Give the correct order of initials T (true) or F (false) for following statements: I. In an anti-fluorite structure, anions form FCC and cations occupy all the tetrahedral voids. II. If the radius of cation and anion is 20 and 95 pm, then the coordination number of cation in the crystal is 4. III. An atom or ion is transferred from a lattice site to an interstitial position in Frenkel defect. IV. Density of crystal always increases due to substitutional impurity defect.
π‘ Solution & Explanation
Statement I: True (anti-fluorite structure, e.g., $Na_2O$, has $O_2$- forming CCP/FCC and Na+ occupying all tetrahedral voids). Statement II: False (radius ratio r_+ / r_- = 20/95 = 0.21, indicating a coordination number of 3, not 4). Statement III: True (by definition of Frenkel defect). Statement IV: False (density can decrease if the substituting atom is lighter than the host atom). Thus, the correct sequence is TFTF.