Answer:
(NH4)2S(aq) + Pb(NO3)2(aq) --> 2NH4NO3 (aq) + PbS (s)
<u>Answer:</u> The correct answer is the mass number of the most common isotope of the element is 24.
<u>Explanation:</u>
We are given:
An element having atomic number 12 is magnesium and atomic mass of the element is 24.305
The image corresponding will be 
The number '24.305' is the average atomic mass of magnesium element.
Average atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.
Formula used to calculate average atomic mass follows:

Average atomic mass of magnesium = 24.305 amu
As, the average atomic mass of magnesium lies closer to the mass of Mg-24 isotope. This means that the relative abundance of this isotope is the highest of all the other isotopes.
The 'Mg-24' isotope is the most common isotope of the given element.
Hence, the correct answer is the mass number of the most common isotope of the element is 24.
This means that they mixed .
<span>The best reason I can think of for why we believe that air is a mixture is that freezing air slowly yields different liquids at different temperatures. Liquid nitrogen has a different boiling point than liquid oxygen. They also freeze at different temperatures. If air were only 1 compound, then air in its entirety would have a single boiling point and a single freezing point. </span>
1 molecule of NaCl contains 1 sodium ion (Na+), that's why if we have 3.0 moles of.
NaCl, we have 3.0 moles of Na+.
N(ions) = n(mol) · NA.
N(ions) = 3.0 moles · 6.02·1023 = 18.06 ·1023 ions.