Hello Pallavi!

Placentation in general terms is 'the arrangement of ovules within the ovary'.

In both tomato and lemon, axile placentation is found. This type of placentation refers to the alignment of ovules along the central axis of a multilocular ovary.
You can refer to Class 11th NCERT textbook of Biology, Chapter 5: Morphology of flowering plants for getting a brief description with illustrations and examples about the 6 various types of placentation in plants.

Feel free to ask in case of any further queries.