Answer
D
Explanation
The conservation of mass principle says that whatever you do to a chemical, the mass of the reactants must equal the mass of the products.
There is a loss somewhere that has not been accounted for.The ribbon and oxygen add up to 6.95 which means that the reactants (oxygen and Magnesium ribbon) added up to more than the mass of the product.
The product was only 6.53 grams. Why that is so is another matter and how they measured the oxygen is still yet something else.
A is wrong. The mass of Mg was measured, it was not calculated.
B is wrong. The experiment really depends on moles not raw mass (which is measured and then converted to mass.)
C is wrong. They are not equal. The products are a little less than the mass of the reactants added together. They do not differ by much, but they do differ.
