shí / ruǐ / yù / dào / suān / xìng / róng / yè / huì / biàn / hóng / yīn / cǐ / cháng / bèi / yòng / zuò / zhǐ / shì / jì

石蕊遇到酸性溶液会变红，因此常被用作指示剂。

Litmus turns red in an acidic solution, so it is often used as an indicator.