Explanation:

- The boundary located at the depth of 2,900 km is known as the core-mantle boundary.

- Option 1: Core-Mantle - This is the correct term. It is the transition zone between the Earth's outer core and the mantle.

- Option 2: Mentle – This seems to be a misspelling of "mantle."

- Option 3: Outersphere – This is not a term used in geology to describe Earth's layers.

- Option 4: Not – Not applicable as a term for Earth's layers.

Option 1: Core-Mantle