Final answer:
Single-parent families are considered the most socially vulnerable due to economic, social, and childcare challenges. Unlike nuclear or extended families, single parents lack broader support systems that can alleviate stress and provide stability.
Step-by-step explanation:
In terms of social vulnerability, single-parent families tend to be the most affected. This structure consists of one parent raising their children alone, and it's becoming more prevalent in various societies. Single-parent families often face economic, social, and childcare challenges that can make them more vulnerable compared to other family structures such as nuclear, extended, or blended families.
The extended family, with its broader support system, and the nuclear family, traditionally consisting of two parents and children, typically have more economic stability and social support. While blended families also experience unique stress due to merging different family backgrounds, the challenges of single parenting, including financial strain and lack of resources, often position these families as most socially vulnerable.