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# The edge length of a face centered cubic cell of an ionic substance is 508 pm .If the radius of the carbon is 110pm , the radius of the anion is

$(a)\;288\;pm\qquad(b)\;398\;pm\qquad(c)\;618\;pm\qquad(d)\;144\;pm$

For an fcc solid, edge length , $a = 2(r^+ + r^-)$
$\Rightarrow2(110 + r^-) = 508$
$\Rightarrow220 + 2r^- = 508$
$\Rightarrow2r^- = 508 - 220$
$\Rightarrow2r^- = 288$
$\therefore r^- = 144pm$
edited Mar 18, 2014