Question

information resulting in the perception of odor is most likely encoded by
receptors specific to a particular odor
receptor groups according to primary odor class
the pattern of activation across many receptors
independent code which doesnt rely on the receptors

Explanation:

The perception of odor is based on the combinatorial activation of multiple olfactory receptors. Each odorant can activate a unique pattern of receptors, and the brain interprets this pattern to perceive the odor. Receptors specific to a single odor (like a "lock - and - key" for one odor) is too simplistic as many odors are complex. Receptor groups by primary odor class is also an oversimplification. And an independent code not relying on receptors is incorrect as receptors are the initial sensory input. The pattern of activation across many receptors is in line with the current understanding of olfactory coding (e.g., the concept of population coding in olfaction).

Answer:

the pattern of activation across many receptors