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Molarity is the amount of moles over 1 L. To figure out the molarity you put

.45 mol / .5 mL multiplied by 1000 mL / 1 L. This gives you the answer of 900 M for molarity. This is extremely high, but with the numbers and units given it is correct.Please let me know if you need any clarification. I'm always happy to answer your questions.