Which equation is balanced?
al+3f2→alf3
na+f2→2naf
2al+3o2→al2o3
2mg+o2→2mgo

2Mg + O2 —> 2MgO

It’s quite simple, really, just add up the total amount of each element on both sides. If there is a difference in the amount of atoms on either side, that equation isn’t balanced.

Take the first equation, Al + 3F2 —> AlF3.
There is one Al atom on each side, so it is properly balanced, but with fluorine, there are 6 on the reactant side and only 3 on the product side. So the entire equation is not properly balanced.
If it wasn’t clear, the 6 fluorine atoms on the products side came from the multiplication of the coefficient on F (3) and the subscript (2). The coefficient 3 basically means there are three molecules of F2.

Its a hope this

Molarity is moles of solute over liters of solution. idk if that is what you are talking about, but you can convert moles of solute to grams of solute using dimensional analyzes by using molar mass found on the periodic table.