To fill in the missing row of the stem-and-leaf diagram, let's first organize the given weights in ascending order:

$1.3, 1.5, 1.9, 2.1, 2.2, 2.2, 2.4, 2.5, 2.9, 3.1, 3.1, 3.3$

The stem-and-leaf diagram should look like this:

• Stem: Represents the whole number part.
• Leaf: Represents the decimal part.

Here's how the diagram should look:

1 | 1 3 5 9
2 | 1 2 2 4 5 9
3 | 1 1 3

So, the missing row for the stem 2 is:

2 | 1 2 2 4 5 9

Would you like any further details or have any questions about this process?

Here are 5 questions you might consider next:

1. How do you handle ties in a stem-and-leaf diagram?
2. Can you create a stem-and-leaf diagram for larger data sets?
3. How would you find the mode from a stem-and-leaf diagram?
4. What are the advantages of using a stem-and-leaf diagram?
5. How do you convert a stem-and-leaf diagram back into a list of numbers?

Tip: Always ensure that the leaves are in ascending order within each stem to make it easier to read and interpret.