Explain why there is a greater increase in effective nuclear charge from left to right across a period than there is for top to bottom in a group.

There is no reason to think the results are biased or not conducted properly but you should not assume the results are correct just because they were done in a laboratory so the answer would be c. it is likely to be reliable because the results support the conclusion presented.

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

It will appear as o2(g) as a reactant