The frames are shown below.
Answer:
Part 1: Starting material = 5X and 8Y, ? = 1X;
Part 2: Starting material = 4X₂ and 3Y₂, ? = 1X₂;
Part 3: Starting material = 4X₂ and 4Y₂, ? = 2X₂;
Part 4: Starting material = 2X₂ and 3Y₂X, ? = X.
Explanation:
Part 1
Each ball represents one atom, thus there are 5X and 8Y as starting materials. In the products there's 4X and 8Y forming 4 Y₂X, so ? = 1X.
Part 2
In this case, there are presented X₂ and Y₂ because the atoms are joined together, so the starting material is 4X₂ and 3Y₂. In the product, there are 6 YX, so it reacts 3X₂ and 3Y₂, and ? = 1 X₂.
Part 3
As in part 2 the atoms are joined together, so there are 4X₂ and 4Y₂. In the product, there are 4Y₂X, so it reacts 2X₂ and 4Y₂, so ? = 2X₂.
Part 4
The starting material now is 2X₂ and 3Y₂X, the product is 3Y₂X₂, so it reacts 3Y₂X and 3/2 X₂, thus ? = 1X.
