Which of the followind pair of solutions can be expected to be isotonic at the same temperature?

1) 0.1M urea and 0.1M NaCl

2) 0.1M NaCl and 0.1M Na2SO4

3) 0.1M Ca(NO3)2 and 0.1M Na2SO4

calculating each osmotic pressure then we get the answer the answer is (3) as for isotonic soln osmotic pressures shud be equal thus formula= Pi=iCRT remove RT as this is constant for all now take i and C for all in 3rd option for 0.1M Ca(NO3)2 i= 3 and C= 0.1 therefore Pi= 0.3 and for 0.1M Na2SO4 i=3 and C=0.1M therefore Pi=0.3 which is equal thus it is isotonic. Hope this helps :)