For diffusion to occur, which condition must be met? a) a concentration gradient must exist. b) a hypotonic external environment is required. c) a hypertonic external environment is required. d) dynamic equilibrium must exist.

A) A concentration gradient must exist.

Explanation:

For diffusion to occur there must be a concentration gradient. Diffusion occurs when particles move from a region of high concentration to a region of lower concentration. Diffusion occurs until there is equal concentration on both sides. Diffusion stops when concentration equilibrium is reached.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements