<h2>Answer : Law of conservation of mass</h2><h3>Explanation :</h3>
The law of conservation of mass states that in any reaction mass is neither created nor lost it has to remain constant in a system.
In this case, when the reaction setup was done in normal way the mass was lost in surrounding was not considered nor being calculated; whereas when the reaction was studied in a closed system where the gas was collected after the reaction the mass changes was noted down which helped to prove the point of law of conservation of mass and energy.
One can consider an example of soda can where the carbonated drink contains pressurized carbon dioxide gas. when opened the gas bubbles gets lost into the surroundings and we don't measure the mass changes. Instead if the soda can was opened in such a way where the gas evolved was measured then the mass changed would remain the same.
Answer: The atomic number is the number of protons in an atom of an element. In our example, krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus.
Then answer would be D. Answer D is correct because you would need to use a better solvent to see the ink separate on the chromatography paper. Hope that helps. :)
