A Fe$-$P liquid alloy is in equilibrium with a solid solution and a gas phase at $1516C.$ The solid

solution behaves ideally and contains two components, CaO and Ca$3$P$208(3$Ca$0.$P$205).$ The P

content in the solid solution is $03\mathrm{.}7wt.\%.$ The gas phase includes $7\mathrm{.}110-10$ atm oxygen. The

activity of $P$ in the alloy, with respect to the $1wt.\%$ in Fe standard state in $Fe$ is $31\mathrm{.}67.$

The given data follows: