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The inverse square law tells us that radiation exposure from a point source drops with the square of the distance. In practical terms, exposure is inversely proportional to the square of how far you are from the source. So if you double the distance, exposure becomes one quarter; if you triple the distance, exposure becomes one ninth. This makes distance a powerful protective factor because small increases in distance yield large reductions in exposure.

Other statements don’t fit because exposure would have to increase with distance if it were directly proportional to distance, which isn’t the case. Saying exposure doubles when distance doubles contradicts the inverse square behavior, and claiming exposure is unaffected by distance ignores the fundamental way radiation spreads from a point source.