Which of the following is a physical change associated with the aging process?

The correct answer is the redistribution of body fat, as it is a well-documented physical change that occurs with aging. As people age, their body composition changes, often resulting in fat being redistributed from areas such as the extremities to the abdominal region. This change can affect one's overall body shape and may also have implications for health, as the location of fat accumulation can influence the risk of various diseases.

The other options illustrate changes that typically do not occur as a person ages. For instance, increased bone density is not a common change during aging; in fact, bone density often decreases, leading to conditions such as osteoporosis. Similarly, increased muscle mass is generally not observed as people age, as there is typically a decline in muscle mass due to factors such as decreased activity levels and hormonal changes. Finally, improved lung capacity is also unlikely; lung capacity tends to decrease with age due to changes in the respiratory system and decreased elasticity of the lung tissue, impacting overall respiratory function.