Which of the following is an example of a significant change in a nursing home resident's condition?

A new medical diagnosis is indeed a significant change in a nursing home resident's condition. This is because a new diagnosis can directly impact the resident's health management, treatment plan, and overall care. It often necessitates adjustments in medication, therapy, and monitoring, which can influence the resident's quality of life and require a reevaluation of their care regimen.

In contrast, other options, while they may indicate changes in the resident's life, do not necessarily reflect a direct alteration in their medical or health status. For instance, a resident moving to a different room could be due to operational reasons or personal preferences and does not inherently affect their health condition. A marked improvement in mobility, while positive, typically indicates an enhancement rather than a significant change, as it doesn't usually indicate deterioration or a new issue that needs addressing. Similarly, changes in meal preferences can result from personal choices or minor health changes but do not signify a substantial shift in medical condition that would require urgent reassessment or intervention.