Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Dissolved substances can be removed from a colloidal solution by diffusion through a parchment paper.
Reason (R) : Particles in a true solution cannot pass through parchment paper but the colloidal particles can pass through the parchment paper.
In the light of the above statements, choose the correct answer from the options given below :

Solution

Chemistry ma’am · 4 steps

In dialysis, small dissolved particles pass through parchment and the colloid stays back. R is reversed.

1. What dialysis is. A colloidal solution is put in a bag of parchment paper (or cellophane) and dipped in water. Dissolved ions and small molecules diffuse out through the membrane, which purifies the colloid. This is dialysis, so (A) is correct.
2. Why it works. Parchment paper has very fine pores. Particles of a true solution, smaller than about 1 nm, pass through them. Colloidal particles, about 1 to 1000 nm, are too big and stay inside.

   Particle	Size	Through parchment paper?
   True solution (ions, small molecules)	below 1 nm	Yes, they diffuse out
   Colloidal particles	1 to 1000 nm	No, they stay in the bag

3. Check the Reason. (R) says true-solution particles cannot pass and colloidal particles can. That is the exact reverse of what happens, so (R) is wrong.
4. So. (A) is correct but (R) is not correct, which is option (c).

The idea to keep. Dialysis is a size filter: parchment and cellophane let small dissolved particles through and hold the bigger colloidal particles back. If the colloid passed through, dialysis could not purify it.

Answer from the NTA final answer key. Solution by PrepWiser.