Final answer:
For natural resources other than oil and gas, the statement regarding percentage depletion that is not true for cost depletion is that it is based on a fixed percentage of gross income. The correct option is (a).
Step-by-step explanation:
The statement regarding natural resources other than oil and gas that is true for percentage depletion but NOT true for cost depletion is: a. It is based on a fixed percentage of gross income. Unlike cost depletion, which considers the actual cost incurred in the extraction of the natural resource, percentage depletion allows for a deduction based on a set percentage of the gross income from the resource regardless of the actual costs incurred.
In contrast, cost depletion considers the actual cost incurred in the extraction process and is limited to a certain percentage of the property's adjusted basis. Cost depletion is based on the actual investment made in acquiring the natural resource property.
This method does not vary with the quantity extracted, nor is it limited to a certain percentage of the property's adjusted basis, which is different from cost depletion.