Passage V

When rocks are melted at very high temperatures beneath Earth's surface, magma (molten rock) is formed. The gases CO2, and H2O can dissolve in magma. Figure 1 shows, for 4 different magmas (leucitite, basanite, rhyolite, and tholeiitic basalt), how the solubility of CO2 in the magma at 1,150°C varies with pressure (in megapascals MPa).

Figure 2 shows, at 3 different pressures, how the solubility of CO2 in rhyolite magma varies with temperature.

Figure 3 shows, at 4 different pressures, how the solubility of CO2, in rhyolite magma at 750°C varies with the weight percent of H2O in the magma.

29. Based on Figure 3, at 750°C and 350 MPa, rhyolite magma having a solubility of CO2, equal to 1, 250 ppmw would most likely have a weight percent of H2O that is:

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

Look at Figure 3, the 350 MPa given in the question is between 300-400 MPa, then first lock the ordinate at 1250, and find that the abscissa corresponding to 300 MPa is about 4.0, and the abscissa corresponding to 400 MPa is close to 6.0, So the range given by option C is reasonable.