Answer:
Parenchyma cells have thin primary walls and usually remain alive after they become mature while Sclerenchyma cells have thick lignified secondary walls and often die when mature.
Parenchyma forms the "filler" tissue in the soft parts of plants while Sclerenchyma provides the main structural support to a plant.
Parenchyma cells are usually loosely packed with large intercellular space while Sclerenchyma cells has no intercellular spaces between the cells.