<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.
Calculating for the moles of H+
1.0 L x (1.00 mole / 1 L ) = 1 mole H+
From the given balanced equation, we can use the stoichiometric ratio to solve for the moles of PbCO3:
1 mole H+ x (1 mole PbCO3 / 2 moles H+) = 0.5 moles PbCO3
Converting the moles of PbCO3 to grams using the molecular weight of PbCO3
0.5 moles PbCO3 x (267 g PbCO3 / 1 mole PbCO3) = 84.5 g PbCO3
It is two or more objects and different things that can be removed from each other.
Isotopes of same element has different number of neutrons with different masses and having same number of protons and electrons.
Radioactive isotopes are those isotopes which are radioactive in nature. The unstable nucleus results in the radioactivity process and this process will go on until the stable isotope (element) forms.
Thus, the nucleus of unstable isotopes of an element will decay leading to emission of radiation.
