Which one of the following is the correct sequence of change in colours when a turmeric stain on white clothes is scrubbed by soap and then washed with water?
- A.Yellow - pink - blue
- B.Yellow - reddish brown - yellow
- C.Yellow - reddish brown - blue
- D.Yellow - blue - pink
Correct answer
Explanation
The correct answer is B, Yellow - reddish brown - yellow. Turmeric is a natural indicator: soap is basic and turns the yellow stain reddish brown, and rinsing with plenty of water removes the soap so the stain turns yellow again.
The colour of turmeric comes from curcumin, which stays yellow in acidic and neutral conditions but turns reddish brown in a basic medium. Soap is made by saponification, the reaction of oils or fats with an alkali such as sodium hydroxide, and its solution in water is basic. When the stain is scrubbed with soap, the base changes curcumin's colour; once water washes the soap away, the medium is neutral again and the yellow returns. NCERT uses this as an everyday example of an indicator.
A is wrong: pink is the colour of phenolphthalein in a base, not of turmeric. C is wrong: the stain does not turn blue after washing; blue is how red litmus responds to a base. D is wrong: turmeric never turns blue or pink.
Exam tip: turmeric turns reddish brown in a base and goes back to yellow when the base is removed or neutralised.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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