Final answer:
The statement about African American liberty and legal protection in Pennsylvania most likely refers to the state's laws for gradual emancipation and Quaker anti-slavery efforts, with the Act for the Gradual Abolition of Slavery in 1780 as a defining piece of legislation. The correct option is - a) Pennsylvania existed as one of the few states that outlawed slavery.
Step-by-step explanation:
The assertion that Pennsylvania was one of the few states in which African Americans 'boasted of rational liberty and protection of the laws' most likely refers to historical developments related to gradual emancipation and the influence of Quaker principles on the law and society.
Specifically, the most accurate reference would be Pennsylvania existed as one of the few states that outlawed slavery through its gradual emancipation laws starting with the Act for the Gradual Abolition of Slavery in 1780, which declared all children born to enslaved mothers after its passage would become indentured servants to be set free at age twenty-eight.
Moreover, Quaker communities in Pennsylvania were influential in pushing for the end of slavery within their borders. We see Quaker ideals of the 'inner light' and the moral contradiction between those beliefs and slavery leading to active anti-slavery efforts, including the creation of the first antislavery society in Philadelphia in 1775.