which is more concentrated 1 molar or 1 molal?
The molarity of a solution is defined as
Molarity = number of moles of solute / volume of solution in Litres
On the other hand, the molality of a solution is defined as
Molality = number of moles of solute / mass of the solvent (in Kg)
Therefore, it actually depends upon the solution whose molality and molarity we are measuring.To be more precise, it will depend upon the density of the solution. More will be the density of a given volume of solution, more will be its mass, and consequently, the concentration of 1 molal solution will be less than one molar solution.
For example, let us consider 1 molar and 1 molal solution of NaCl in water. Both will contain 1 mole of NaCl. However, in 1 molar solution there will be 1 litre of solution, where as in 1 molal solution there will be 1 Kg of water. So if the density of 1 litre aqueous solution of NaCl is more than 1 g/cc, its mass would be more than 1 Kg and hence the molality of 1 molar NaCl solution would be less than that of one molal NaCl solution.
Similarly, if the density of aqueous solution is less than 1 g/cc, its mass would be less than 1 Kg, and hence the molality of 1 Molar NaCl would be more than 1 molal NaCl solution.