In the reaction mg (s) + 2hcl (aq) h2 (g) + mgcl2 (aq), how many grams of hydrogen gas will be produced from 125.0 milliliters of a 6.0 m hcl in an excess of mg?

The balanced reaction is: 

We are given the amount of  reactants to be reacted. This will be the starting point of the calculations.

.125 L HCl solution (6.0 mol HCl / L solution) ( 1 mol H2 / 2 mol HCl ) ( 2.02 g H2 / 1 mol H2 ) = 0.76 g H2

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of c is as shown here in the image.