Scientists should control most possible variables in experiments to get the most valid and correct data. If many variables are included in experiments it is more difficult to interpret what is causing a different outcome.
In 1 mole of propane, there are 44 grams
so, X moles = 6.2 grams
Cross multiply: 44x = 6.2
x = 0.14 moles
(In scientific notation) The answer is B