Answer: Option (b)
Isotonic solutions are those which have same osmotic pressure and hence same molar concentration. We know that osmotic pressure,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_4710b195-7ee8-4279-bc24-109f403080c020180806-4918-u33s0b.svg)
=i CRT
where i = total no. of ions in the electrolyte solution.
Option (a) 0.1 M Urea.
Urea does not ionize.
So,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_7120bf9d-ac12-4ec7-a9e1-135d5f7b3e0a20180806-4918-1pgkfqf.svg)
= CRT = 0.1 RT
0.1 M NaCl.
![NaCl rightwards harpoon over leftwards harpoon stack Na to the power of plus with 1 space ion below plus stack Cl to the power of minus with 1 space ion below](https://search-static.byjusweb.com/question-images/byjus/_e37eb67c-c074-494d-92e2-89c915ab309220180806-4918-112amed.svg)
i = 1 + 1 = 2
![therefore straight pi](https://search-static.byjusweb.com/question-images/byjus/_fe360d2b-0b0f-4290-935a-13655c8bb19320180806-4918-gckc8x.svg)
= i CRT = 2 × 0.1 RT = 0.2 RT
Since, 0.1 RT and 0.2 RT differ, these are not isotonic solutions.
Option (b) 0.1 M Glucose
Glucose does not ionize. So,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_f1572f02-643b-4117-b385-d7989d75f21820180806-4918-s28z7g.svg)
= CRT = 0.1 RT
Urea (0.1 M) does not ionize.
So,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_e6597f11-5d97-406d-a838-9749caf1d9c520180806-4918-1j1r12a.svg)
= CRT = 0.1 RT
Hence, 0.1 RT and 0.1 RT are same, these are isotonic solutions. Option (c) 0.02 M
![therefore](https://search-static.byjusweb.com/question-images/byjus/_896d1403-125d-4803-979f-19c7e9e5332720180806-4918-v78g9h.svg)
i = 1+ 1 = 2
![therefore](https://search-static.byjusweb.com/question-images/byjus/_d34f71fd-15ca-4276-99a2-470d131c141420180806-4918-8pg6sy.svg)
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_50c92033-4f22-48cf-ac71-3dde4eb6fb0820180806-4918-1qg3kr3.svg)
= 2 × 0.02 RT = 0.04 RT
Urea (0.1 M) does not ionize.
So,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_9061664e-701e-436a-8745-0f801f55efcd20180806-4918-3qzyho.svg)
= CRT = 0.1 RT
Since 0.04 RT and 0.1 RT differ, these are not isotonic solutions.
Option (d) 0.1 M
![therefore](https://search-static.byjusweb.com/question-images/byjus/_e0cdbde1-d31e-4876-801d-f0ddd4b6628920180806-4918-1kslv19.svg)
i = 1+ 2 = 3
![therefore](https://search-static.byjusweb.com/question-images/byjus/_dad79679-08be-4961-8c69-6e5acc1634f120180806-4918-2txs3a.svg)
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_f664dc91-55b0-4265-937d-06a0865e4d3620180806-4918-1h1aahw.svg)
= 3 × 0.1 RT = 0.3 RT
Urea (0.1 M) does not ionize.
So,
![straight pi](https://search-static.byjusweb.com/question-images/byjus/_28a9c2c4-8ec1-44a5-a238-446ab0dc134420180806-4918-1c1xl4.svg)
= CRT = 0.1 RT
Since 0.3 RT and 0.1 RT differ, these are not isotonic solutions.