Answer: The missing coefficient is 2.
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

As in the products, there are 2 atoms of sodium, thus there will be 2 atoms of of sodium in the reactant as well. This will balance the number of hydrogen and oxygen atoms as well.
Thus the missing coefficient is 2.
K. Ionization energy increases as you go up and to the right, and k is the furthest left and furthest down
Mole-mole calculations are not the only type of calculations that can be performed using balanced chemical equations. Recall that the molar mass can be determined from a chemical formula and used as a conversion factor. We can add that conversion factor as another step in a calculation to make a mole-mass calculation, where we start with a given number of moles of a substance and calculate the mass of another substance involved in the chemical equation, or vice versa.
For example, suppose we have the balanced chemical equation
2 Al + 3 Cl 2 → 2 Alcoa
Suppose we know we have 123.2 g of Cl 2. How can we determine how many moles of Alcoa we will get when the reaction is complete? First and foremost, chemical equations are not balanced in terms of grams; they are balanced in terms of moles. So to use the balanced chemical equation to relate an amount of Cl 2 to an amount of Alcoa, we need to convert the given amount of Cl 2 into moles. We know how to do this by simply using the molar mass of Cl 2 as a conversion factor. The molar mass of Cl 2 (which we get from the atomic mass of Cl from the periodic table) is 70.90 g/mil. We must invert this fraction so that the units cancel properly:
Answer:
As^3-, Se^2-, Br^-, Rb^+, Sr^2+
Explanation: