Fluorine gas is placed in contact with calcium metal at high temperatures to produce calcium fluoride powder. What is the formula equation for this reaction?

Calcium forms Ca²⁺ ions and fluorine forms F⁻ ions, so the product is calcium fluoride, CaF₂. One F₂ molecule supplies the two fluorine atoms needed for each calcium atom, giving the balanced equation F₂(g) + Ca(s) → CaF₂(s), with heat indicated above the arrow. This matches choice D.

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