Answer:
It happens because turmeric is a natural indicator for bases.
Step-by-step explanation:
Turmeric acts as an indicator for any basic substance. On coming in contact with a basic substance it turns red, hence indicating that the substance is basic.
Turmeric is a natural indicator for bases.
Soap solution is basic in nature.
When we try to remove the turmeric stain from the dress with soap, the turmeric comes in contact with the soap and turns red.
Purple Cabbage is also another natural indicator for both acids and bases. It turns reddish-pink in acidic solutions and in a basic solution, it turns bluish green.