Which organelle is responsible for breaking down the cells that once made up the tail of the tadpole?

The cells present in the tail of the tadpole undergo a programme cell death. This is made possible when the organelles called lysosomes present in the cells break open to cause the breakdown and digestion of all the components of the cells. The lysosomes are break open only when the cells receive a signal from their neighbouring cells to undergo apoptosis, a process where the cell kills itself.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added