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Equilibrium constants are given (in atm) for the following reactions at \( 0^{\circ} \mathrm{C} \) :
\[
\begin{array}{ll}
\mathrm{SrCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \rightleftharpoons \mathrm{SrCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) & \mathrm{K}_{\mathrm{p}}=5 \times 10^{-12} \\
\mathrm{Na}_{2} \mathrm{HPO}_{4} \cdot 12 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \rightleftharpoons \mathrm{Na}_{2} \mathrm{HPO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}(\mathrm{s})+5 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) & \mathrm{K}_{\mathrm{p}}=2.43 \times 10^{-13} \\
\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \rightleftharpoons \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{~s})+10 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) & \mathrm{K}_{\mathrm{p}}=1.024 \times 10^{-27}
\end{array}
\]
\( \mathrm{P} \) The vapor pressure of water at \( 0^{\circ} \mathrm{C} \) is \( 4.56 \) torr.
At what relative humidities will \( \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O} \) be efflorescent (release moisture) when exposed to air at \( 0^{\circ} \mathrm{C} \) ?
(A) above \( 33.33 \% \)
(B) below \( 33.33 \% \)
(C) above \( 66.66 \% \)
(D) below \( 66.66 \% \)
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