The correct option is C 285
According to Henry's Law,
P=KH×χ
KH=Henry's constant,χ=mol fraction
At STP, P = 1 atm
0.195 m means 0.195 mol of gas is dissolved in 1 kg of solvent (water)
nH2O=1000 g18 g mol−1
Mol fraction of H2S=nH2SnH2S+nH2O
χH2S=0.1950.195+100018=0.0035⇒P=KH×χ⇒KH=1.000.0035≈285.7 atm