(1) What is the formula of a compound that crystallizes with fluoride ions occupying all of the tetrahedral holes in a FCC array of calcium ions?
(2) What is the formula of a compound that crystallizes with copper ions occupying one-half of the tetrahedral holes in a FCC array of fluoride ions?
(3) Suppose you wanted to make a compound that is isoelectronic with Ge. You replace 50% of the Ge atoms with Ga, and 25% of the other Ge atoms with As. Name an element (or elements) you could use to replace the final remaining 25% of the Ge atoms with to give you a compound isoelectronic with Ge.