Converting units and sig figs (finding molarity)?
In terms of significant figures, you always use the number with least amount of sig figs to determine how many sig figs your answer has. In this case, one number has 3 sig figs, and the other has 1. Therefore your answer should have 1 sig fig and be 1 mol/L, as you said. To make the zeroes in the 500 mL become significant it would need to have a period afterwards like this: 500. mL. Perhaps the writer forgot to do that, however as it is written the answer would be 1 sig fig: 1 mol/L