A 100-g sample of zinc sulfide contains 67.1 g zinc and 32.9 g sulfur. If a 1.19-g sample of zinc is heated with excess sulfur, 1.77 g of zinc sulfide forms. Are these data in agreement with the law of definite proportions?

As per the law of definite proportion a chemical compound will always contain the same elements that combine together in the same ratio by mass.

In case 1:

Mass of Zinc sulfide sample = 100 g

Mass of Zn = 67.1 g

Mass of sulfur = 32.9 g

Ratio Zn : S = 67.1 : 32.9 = 2:1

In case 2:

Mass of zinc sulfide formed = 1.77 g

Mass of Zinc taken = 1.19 g

Mass of sulfur = 1.77 - 1.19 = 0.58 g

Ratio Zn:S = 1.19 : 0.58 = 2:1

Since the ratio in both cases are the same, the data is in agreement with the law of definite proportion.