Q. Assertion: One molar aqueous solution has always higher concentration than one molal.
Reason: The molality of a solution depends upon the density of the solution whereas molarity does not.

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Solution:

In one molar aqueous solution, one mole solute is present in of solution while in case of one molal solution, one mole solute is present in of solvent. Thus, former one is more concentrated if solvent is water.
Molality depends upon mass of solvent which in turn is calculated by finding mass of solution for which density is required while molarity depends upon volume of solution, thus density is not required to calculate it.
Hence, both Assertion and Reason are correct.