In determining the formula of a hydrate through heating, what is the significance of the value "X" in the expression CuSO4 (XH2O)?
A) The molar mass of CuSO4
B) The number of moles of CuSO4 per mole of water
C) The molar mass of water (H2O)
D) The ratio of moles of water to moles of CuSO4