After you have dinner tonight, wash your own plate with soap / detergent. (1) What colour change is observed, when soap / detergent is applied? (2) Name the type of reaction and explain it.

Ans. 

(1) On applying soap / detergent, the yellow oily stains turn red / orange. 

(2) Turmeric (Yellow colour) changes to  red / orange due to the neutralization reaction. Edible oils are compounds of alcohols and organic acids, which get neutralized by alkaline soap/detergent. this neutralization reaction is indicated by turmeric (yellow) which turns red.