Which element has six valence electrons in the 4th outer shell?

Does anyone know a lot about how to: - calculate mass of magnesium metal - calculate the actual yield of magnesium oxide - calculate the theoretical yield of mgo - calculate the percent yield of mgo - determine the percent yield of mgo - determine the average percent yield of mgo i had to do an online lab and its asking these questions but i have no idea where to start or how to be able to find these things. i can post the chart of the data from the lab or if you can tell me exactly how i can find each.

If you have 5.25 grams of methane (ch4), how many grams of co2 will you produce ?

What will most likely happen when two bromine atoms bond together?