The answer that is not a physical factor affecting depreciation is C. obsolescence, as it pertains to assets becoming outdated due to technological or market changes, not physical deterioration.
Out of the listed options, the one that is not a physical factor affecting depreciation is C. obsolescence. Depreciation is the process by which an asset loses value over time due to various factors. Physical factors that contribute to depreciation include casualties, like damage from accidents or natural disasters; decay, which is deterioration as a result of age or environmental conditions; and wear and tear, which happens through regular use.
On the other hand, obsolescence refers to the asset becoming outdated or less valuable because of technological advancements or changes in market preferences, which is not a physical factor.
Therefore, the correct answer to the student's question is C. obsolescence, as it is not a physical factor but an economic factor that influences the depreciation of an asset. This is important in understanding how various factors contribute differently to the decrease in an asset's value over time.