Calcium + Phosphorous to produce Calcium Phosphide is an ionic synthesis reaction.

Calcium has a charge of ##Ca^(+2)##.Phosphorous has a charge of ##P^-3##. To bond these two ions together, their charges must be equal and opposite. Therefore we need 3 ##Ca^(+2)## ions to balance with 2 ##P^-3## in order to balance their charges at 6 for the molecule ##Ca_3P_2##.

##3Ca + 2P -> Ca_3P_2##

I hope this was helpful. SMARTERTEACHER

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