Correct Answer: lichen

Solution : The correct option is lichen.

Litmus is a water-soluble natural dye extracted from lichens, which are symbiotic organisms composed of a fungus and an alga or cyanobacterium. Specifically, litmus is obtained from certain species of lichens, such as Roccella tinctoria and related varieties. The lichen containing litmus are typically found in regions with a humid climate. Litmus has been used as a pH indicator, meaning it changes color depending on whether a substance is acidic or basic (alkaline). In acidic solutions, litmus turns red, while in alkaline solutions, it turns blue.