Given the balanced equation: 2H2 + 02 --> 2H20

How many grams of H20 is produced if you have 7g of O2

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

Idont know. if you want an answer you need to give us some context dude.

Answer(2) electrons;