Celery stalks that are immersed in fresh water for several hours become stiff and hard. similar stalks left in a salt solution become limp and soft. from this we can deduce that the cells of the celery stalks are

a. hypotonic to both fresh water and the salt solution.
b. hypertonic to both fresh water and the salt solution.
c. hypertonic to fresh water but hypotonic to the salt solution.
d. hypotonic to fresh water but hypertonic to the salt solution.
e. isotonic with fresh water but hypotonic to the salt solution.

C

Explanation:

The Celery stalks are hypertonic to fresh water but hypotonic to the salt solution

When Celery stalks that are immersed in fresh water for several hours become stiff and hard. This means that the cells of the celery stalks contain more concentrated solute relative to lower concentration in fresh water. Hence by osmosis water will move into the celery stalks which makes it to swell and hard.

But when the celery stalks are left in a salt solution become limp and soft. This is because the solution in the stalks contain less solute relative to the salt solution(more solute). Therefore water will move from lower concentration to higher concentration by osmosis. This makes the celery stalks loose water and become limp and solf because it's cells is shrinking.

that is wrong, its not thymus.