<span>As new discoveries are made, existing theories are revised or replaced.</span>
        
                    
             
        
        
        
Answer: Potassium 
Explanation: Potassium is the chemical element with 19 electrons, 19 protons and 20 neutrons.
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Answer:
Mass = 12.276 g
Explanation:
Given data:
Number of molecules of H₂S = 2.16 × 10²³
Mass in gram = ?
Solution:
The given problem will solve by using Avogadro number.
It is the number of atoms , ions and molecules in one gram atom of element, one gram molecules of compound and one gram ions of a substance.
The number 6.022 × 10²³ is called Avogadro number.
For example,
18 g of water = 1 mole = 6.022 × 10²³ molecules of water
Number of moles of  H₂S:
2.16 × 10²³ molecules × 1 mole /6.022 × 10²³ molecules 
0.36 moles
Mass = number of moles ×  molar mass
Mass = 0.36 mol × 34.1 g/mol
Mass = 12.276 g
 
        
             
        
        
        
The molar mass of monotonic Nitrogen is 14 g/mol. Since this is diatomic Nitrogen, double that to 28 g/mol.
Next, divide total mass by molar mass, 500 g / 28 g/mol, which gives <span>17.8571 moles. A mole is defined as being 6.022*10^23 molecules, so multiply moles by molecules/mol (Avogadro's number), and we finally end up with something like 1.075 * 10^25, give or take a few billion particles.</span>
        
             
        
        
        
It’s option B 0.0821L.atm/mol.K