Explanation:
Density
It is defined as mass per unit volume for a given substance .
Its formula is D=M/V
Its unit is =kg/m³
In the above asked question :
Mass of gaseous chlorine = ?
Volume of gaseous chlorine = 125 ml =125/1000=0.125L
Density = 3.16 g/L
D=M/V
M=V x D
M=0.125 x 3.16
M= 0.395 g