Partial molal quantities are important in the study of

Answer: Option C

Partial molar properties are defined as in non ideal systems the molar properties of an component in an mixture is not equal to molar properties of the same component when present as pure component so as to designate the properties of individual components in the mixture we used partial molar properties.
These partial molar properties and the total mixture property is related as $$M^t=\sum x_i\overline{M_l}$$