Question

for diffusion to occur, which condition must be met?
a concentration gradient must exist.
a hypotonic external environment must exist.
a hypertonic external environment must exist.
dynamic equilibrium must exist.

Explanation:

Diffusion is the movement of substances from an area of higher concentration to an area of lower concentration. A concentration gradient, which is a difference in concentration of a substance across a space, is essential for this movement to occur. Hypotonic or hypertonic environments relate more to osmosis (water - specific diffusion) and dynamic equilibrium is the end - state of diffusion, not a requirement for it to start.

Answer:

A. A concentration gradient must exist.