How many EDTA (ethylenediaminetetraacetic acid) molecules are required to make an octahedral complex with a $C{a}^{2+}$  ion?

EDTA is hexadentate (four donor O atoms and 2 donor N atoms and for the formation of octahedral complex one molecule is required

$C{a}^{++}+\left[H_{2}EDT{A}^{-}\right]\to {\left[Ca\right(EDTA\left)\right]}^{2-}+2H^{+}$