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If the unit cell of a mineral has cubic close packed (ccp) array of oxygen atoms with m fraction of octahedral holes occupied by aluminium ions and n fraction of tetrahedral holes occupied by magnesiums ions, m and n respectively, areA. `1/2, 1/8`B. `1, 1/4`C. `1/2, 1/2`D. `1/4, 1/8` |
Answer» Correct Answer - A For ccp arrangement , `Z=4` `:.` No. of oxygen (O) atoms present `=4` No. of octahedral voids `=4` No. of tetrahedral voids `=2xx4=8` No. `Al^(3+)` ions `=mxx4` No. of `Mg^(2+)` ions `=nxx8` The formula of mineral `=Al_(4m)Mg_(n8)O_(4)` `4m(+3)+8n(+2)+4(-2)=0` or `3m+4n-2=0` or `3m+4n=2` The possible values of m and n are `1//2` and `1//8` respectively Substituting these values `(3xx1/2)+(4xx1/8)=2` |
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