Which of the solution below is isoosmotic

Question

100 mm of nacl 

300 mm of nacl 

250 mm of dextrose 

150 mm nacl 

500 mm calcl2 

 

my answer is 3 rd one but I want to make sure I am right. Is it because calculation osmolarity dextrose does not dissociate ? 

Answer 1

As I mentioned in a previous comment, isosmotic, hyper and hypo have to have a reference point.  Assuming we are talking about most mammalian cells, that reference would be approximately 320 mOsM (0.32 OsM).  Also, we'll assume that you mean 100 mM (not 100 mm) NaCl, etc. in you question.  Thus, we have the following:

100 mM NaCl = 200 mOsM (hypotonic)

300 mM NaCl = 600 mOsM (hypertonic)

250 mM dextrose = 250 mOsM (hypotonic)

150 mM NaCl = 300 mOsM (isotonic)

500 mM CaCl2 =1500 mOsM (hypertonic)

 

So, the answer should probably be the 4th one.