Final answer:
Li₃P is the compound that is soluble in water because compounds of Group 1 elements like lithium are generally soluble. Li3P is soluble in water according to the solubility rules.
Step-by-step explanation:
The question asks which of the given compounds is soluble in water. According to solubility rules provided in educational resources, we know that all compounds of Group 1 elements (Li+, Na+, K+, etc.) are generally soluble in water.
Given this rule, out of the options provided (Sc2O3, Li3P, CuS, Hg2I2), Li3P, which contains the lithium cation (Li+), would be the soluble compound in water. Li₃P is the compound that is soluble in water because compounds of Group 1 elements like lithium are generally soluble. Li3P is soluble in water according to the solubility rules.