At 27 degrees Celsius and 750 mm Hg, a sample of hydrogen occupies 5.00 L. The space it occupies at STP = 4.49 L.

Should the 4.49 L be rounded to 4.5 L? If not, is there a specific rule that explains rounding for this type of problem?

In multiplication and division, which is all you have in this problem, the rule is that you may have as many significant figures in the answer as you have in any of the numbers. So where did the 4.49 come from?

5.00 x (750/760) x (273./300.) = 4.49. You're allowed 3 s.f., you have 3 s.f., you don't need to round anything.
Here is a very good site that explains about significant figures.
http://www.chemteam.info/SigFigs/SigFigs.html

To determine whether the value 4.49 L should be rounded to 4.5 L or not, we need to understand the specific rules for rounding in this type of problem.

In general, when rounding a decimal number to a certain number of decimal places, the following rules apply:

1. If the digit to the right of the last decimal place to be kept is less than 5, we simply drop all digits to the right of that place.

Example: 3.14159 rounded to two decimal places = 3.14

2. If the digit to the right of the last decimal place to be kept is 5 or greater, we increase the value in the last kept decimal place by 1.

Example: 3.1459 rounded to two decimal places = 3.15

Now let's apply these rules to determine whether 4.49 L should be rounded to 4.5 L:

Since the last decimal place in 4.49 L is 9, which is greater than 5, we would increase the value in the last kept decimal place by 1. Therefore, when rounding to two decimal places, 4.49 L would be rounded to 4.50 L.

So, to answer your question, the value 4.49 L should be rounded to 4.50 L (not 4.5 L) according to the rules of rounding.

Please note that in some cases, rounding may depend on the context or specific instructions provided. It is always a good idea to refer to any guidelines or instructions given to determine the appropriate rounding in a particular problem.

To determine whether the value 4.49 L should be rounded to 4.5 L or not, we need to consider the rules for rounding in scientific measurements.

In scientific measurements, there are generally two rules for rounding:

1. If the digit to be dropped is less than 5, round down (keep the preceding digit unchanged).
2. If the digit to be dropped is 5 or greater, round up (increase the preceding digit by one).

In this case, we have 4.49 L. Since the digit to be dropped (9) is greater than 5, we apply rule 2 and round up.

Therefore, the correct rounding would be to round 4.49 L to 4.5 L.