Which would have the higher osmotic pressure: a 0.10 M solution of NaCl or a 0.10 M solution of KBr?

Osmotic pressure is calculated by multiplying the molarity, temperature and the universal gas constant. It is expressed as:

P = iMRT

Say the temperature for both solutions is 373.15 K.

P (NaCl) = 2 x 0.10 x 0.08206 x 373.15 = 3.06 atm

P (KBr) = 2 x 0.10 x 0.08206 x 373.15 = 3.06 atm

They will have the same osmotic pressure since they have the same concentration, dissociate into 2 ions and at the same temperature.