Final answer:
The situation described is an example of curable external obsolescence, where homeowners on the block have failed to maintain their properties. This can be rectified by improving the upkeep of the properties.
Step-by-step explanation:
The situation described in the question is an example of curable external obsolescence. External obsolescence refers to factors outside of the property itself that negatively affect its value. In this case, the failure of homeowners on the block to maintain their properties is a curable condition that can be rectified by the homeowners improving the upkeep of their properties. This can lead to an improvement in the overall neighborhood and increase the value of the homes.