No, it isn't a state. It is a district.
The border state of Maryland remained in the Union during the US Civil War and was a slave holding state. Washington DC is surrounded by Maryland and by the Potomac River.
Under the Missouri Compromise of 1820 Missouri was admitted as a slave state and Maine as a free state.
Compromise of 1850
That was called the Compromise of 1850.
The Compromise of 1850 abolished slavery in the state of Washington DC. It also allowed California to become part of the union as a slave free state.
The Potomac divided the Confederacy from the Union, although Maryland was a slave-state, and so was DC at the beginning. The Ohio River divided the slave-states from free soil.
DC refers to the District of Columbia, which is not a state.
Slave state
Mississippi was a slave state until the end of the Civil War.
Wisconsin was not a slave state.
no canada was not a slave state
it was a free state >3