Verified Answer :

MathiasCZR01

You have 12.5 grams. And 5 liters of some random gas. 

Step 1: You must find the mol amount of that 12.5g mass. 

12.5 / 5 = 2.5 mol 

Step 2: Now find the molecular mass of that gas "at STP" (STP- is 22.4 L) 

2.5 x 22.4 = 56 g/mol

Good Luck on Chemistry SAT, cause I know exactly where you got this question from.

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