Step 1: Understand placentation.
Placentation tells us where the ovules (future seeds) are attached inside the ovary of a flower. There are several patterns, each with typical plant examples.
Step 2: Recall parietal placentation.
In parietal type, the ovules grow on the inner walls or the side parts of the ovary. A common example is $Mustard$.
Step 3: Check the mustard option.
The option that says ovules develop on the inner walls of the ovary in Mustard exactly describes parietal placentation, so this statement is correct.
Step 4: Test the Dianthus claim.
Dianthus actually shows free-central placentation, where ovules grow on a central column without partitions. So calling it axile is wrong.
Step 5: Test China rose and Pea claims.
China rose shows axile placentation, not free-central. Pea shows marginal placentation, not basal. So both these statements are incorrect.
Step 6: Conclude.
Only the Mustard statement correctly matches its placentation type, so that is the right choice.
\[ \boxed{\text{Ovules develop on inner walls/peripheral part of the ovary - Mustard}} \]