Final answer:
The word that best describes the mood of Dr. Martin Luther King's speech at the 1963 March on Washington is reassuring.
Step-by-step explanation:
The word that best describes the mood of Dr. Martin Luther King's speech at the 1963 March on Washington is reassuring. In his speech, Dr. King spoke about the promises made by the architects of the Constitution and the Declaration of Independence, and emphasized that these promises included the guarantee of unalienable rights for all Americans, regardless of race. By referring to these promises, Dr. King sought to reassure the audience that their struggle for civil rights was justified and that they would eventually achieve equality.