Given $NaSO_4.10H_2O (s) \rightleftharpoons NaSO_4 (s) + 10H_2O (g) ; K_p =4.08 \times 10^{-25}$ and vapour pressure of water at $0^\circ$C = 4.58 Torr. At what relative humidity will $Na_2SO_4$ be deliquescent when exposed to the air at $0^\circ$C ?

Question

(a) below 60.5%

(b) above 60.5%

(c) above 39.5%

(d) below 39.5%