Osmolarity of 4.2% solution of sodium bicarbonate is ?

Ans. is 'b' i.e., 1000 osmole/litre4.2% solution of sodium bicarbonate contains 0.5 mmol/mL (or 500 mmol/ml).This solution will have osmoloarity 1000 mOsm/L (as solution contains two active osmoles, i.e., 500 mOsmole of Na+ and 500 mOsmole of HCO3-).One mole of osmotically active paicles is called one osmole. In case of non-dissociated solutes, one gram molecular weight of any substance contain similar number of osmotically active molecules (osmoles), thus a molar solution of glucose contains 1 osmole. On the other hand, in case of dissociated solutes, one gram molecular weight of any substance contain the number of osmotically active molecules (osmoles) equal to the number of dissociated molecules, e.g., a molar solution of NaCl contains 2 osmoles (1 mole of Na+ and 1 mole of C1--). The osmolar concentration of a solution in osmole/litre is called osmolarity. When expressed in osmole/Kg of solution is called osmolality.