The number above the symbol is the atomic mass (or atomic weight). This is the total number of protons and neutrons in an atom. The number below the symbol is the atomic number and this reflects the number of protons in the nucleus of each element's atom. Every element has a unique atomic number.
A decrease in the total volume of the reaction vessel (T constant)
Explanation:
Le Châtelier's principle predicts that the moles of H2 in the reaction container will increase with a decrease in the total volume of the reaction vessel.
<em><u>According to the Le Chatelier's principle, when a chnage is a applied to a system at equilibrium, then the equilibrium will shift in a way that counteracts the effect causing it.</u></em>
In this case, a decrease in volume means there is an increase in pressure, therefore the equilibrium will shift towards the side with the fewer number of moles of gas.