Five liters of gas at stp have a mass of 12.5 g. what is the molecular mass of the gas?
a. 12.5 g/mol
b. 25.0 g/mol
c. 47.5 g/mol
d. 56.0 g/mol
e. 125 g/mol

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. 

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

Idon't see the pic?