The incorrect statement about rubber is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Rubber particles are positively charged
Latex is a colloidal solution of rubber particles in water. The rubber particles carry a negative charge. Adding positive ions (for example an acid) neutralises this charge, the particles come together, and rubber separates.
Option (1) Latex is a colloidal solution of rubber particles — A correct statement about rubber. Latex from the rubber tree is rubber dispersed in water as colloidal particles.
Option (2) Rubber particles are negatively charged — A correct statement about rubber. This charge keeps the particles apart, so latex stays as a stable sol.
Option (3) Rubber particles are positively charged — An incorrect statement about rubber. The particles in latex are negatively charged, not positively; that is why latex is coagulated by positive ions.
Option (4) Rubber is obtained by coagulation of latex — A correct statement about rubber. When the charge on the particles is neutralised they coagulate, and natural rubber is obtained.
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):
Applications of Colloids – …
