A certain substance X melts at a temperature of −9.9°C . But if a 350g sample of X is prepared with 31.8g of urea NH22CO dissolved in it, the sample is found to have a melting point of −13.2°C instead.
a. Calculate the molal freezing point depression constant Kf of X . Round your answer to 2 significant digits.

the molal freezing point depression constant Kf of X  = 2.18 degree celsius

Explanation:

The step by step calculation using the relationship between the depression of freezing point and the molal concentration is as shown in the attachment.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3