Answer: Option (b) is the correct answer.
Step-by-step explanation:
According to law of conservation of mass, mass can neither be created nor it can be destroyed. It can only be changed from one form to another.
For example, when 137 g of barium reacts with x grams of iodine to produce 391 g barium iodide.
Then mass of iodine will be calculated as follows.
Total mass of reactants = total mass of products
137 g + x = 391 g
x = 391 g - 137 g
= 254 g
Thus, we can conclude that 137 g of barium reacts with 254 g iodine to produce 391 g barium iodide.