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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ss147

The radius ratio rule is applied to four ionic compounds (all radii in pm). Which predictions are correct?

A $r_{+} = 70$ , $r_{-} = 140$ : octahedral voids, coordination number 6.
B $r_{+} = 30$ , $r_{-} = 140$ : coordination number 3.
C $r_{+} = 110$ , $r_{-} = 140$ : coordination number 6.
D $r_{+} = 50$ , $r_{-} = 140$ : coordination number 4.

Answer: A, B, D

Ratios:

70/140 = 0.500

(0.414-0.732, CN 6);

30/140 = 0.214

(0.155-0.225, CN 3);

110/140 = 0.786

(above 0.732, CN 8, so C is wrong);

50/140 = 0.357

(0.225-0.414, CN 4).

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