Which of the following substance/s will precipitate the emulsion which is negatively charged?
A. \(KCl\)
B. \(Glucose\)
C. \(NaCl\)
D. \(Urea\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, C only
The cations of an added electrolyte neutralise the negative charge on the droplets, and they coalesce; a non-electrolyte gives no ions.
(A) KCl — an electrolyte (\( \ce{K^{+}} \) + \( \ce{Cl^{-}} \)); \( \ce{K^{+}} \) neutralises the negative droplets. Precipitates.
(B) Glucose — a non-electrolyte; gives no ions. Does not precipitate.
(C) NaCl — an electrolyte (\( \ce{Na^{+}} \) + \( \ce{Cl^{-}} \)). Precipitates.
(D) Urea — a non-electrolyte. Does not precipitate.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Emulsions – “… The droplets in emulsions are often negatively charged and can be precipitated by electrolytes.”