Final answer:
Option (D), David Walker is the abolitionist who wrote the radical and powerful pamphlet 'An Appeal... to the Colored Citizens of the World', which condemned racism and called for the immediate end of slavery.
Step-by-step explanation:
The abolitionist who condemned racism in the pamphlet "An Appeal... to the Colored Citizens of the World" is David Walker. Walker's work was a forceful and radical plea for the humanity of Black people and the immediate end of slavery. He encouraged Black people to resist slavery actively and to fight for equality in the United States.
Published in 1829, Walker's Appeal highlighted the nation's hypocrisy regarding freedom and slavery, and he criticized some Christians' complicity in the system of slavery. His words had a profound impact, instilling hope in the free people of the North and striking fear in the hearts of Southern slaveholders.