Which of the following are used as black pigment in black ink?

Pigments are materials with a strong colour that are used to give other things colour. Typically, pigments are totally or almost completely soluble in water. Chemicals called pigments are inorganic.

The dark pigment carbon black is widely used. Carbon black is also used to provide the black colour of black ink.

Burning heavy petroleum compounds like coal tar, FCC tar, and ethylene cracking tar in the atmosphere is the primary method of producing carbon black. Vegetable oil can also be used to make it in modest quantities. Carbon black is made up of solid, opaque particles that are coloured by being suspended in ink. In crystalline structures that range in size from 0.1 to 2 nm and take up between 5 and 30 percent of the entire volume of the ink, pigment molecules are joined together. The source and kind of the pigment affect other ink characteristics including saturation, colour, and brightness.

Hence, option A is correct.