Why does 225.0 have 3 significant figures, not 4?

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i_love_science
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What are the number of significant figures of 225.0? I think it is 4, but the solution says it's 3.

Also, is the significant figures of molar volume at STP (22.7 L/mol) considered? Thanks.
 
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A super-duper quick Google (which doesn't count here) agrees with my understanding:
  • Trailing zeros to the right of the decimal ARE significant. ...
  • Trailing zeros in a whole number with the decimal shown ARE significant.
That suggests you are right. I'd take it up with your instructor.
 
225.0 has four significant figures. Why did you include the zero in your answer? Did you round it from something like, 225.0173946289?
It sounds like it was part of a calculation and unless we see that calculation, we can’t tell you what is correct!
 
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Molar volume of gas at STP can be calculated from the ideal gas equation. As of today all numbers in that equation - including R, ideal gas constant - are defined, that is, they have infinite number of significant digits (you can put as many zeros at the end as you need). That means it is possible to calculate molar volume with infinite accuracy.

It wasn't always this way, R used to be a measured quantity, with known experimental error.