Moles of nitrogen = 49.84 / 28 = 1.78
Moles of hydrogen = 10.7 / 2 = 5.35
Molar ratio of nitrogen to hydrogen = 1 : 3
Hydrogen required = 1.78 x 3 = 5.34
Therefore, hydrogen is in excess and nitrogen is the limiting reagent.
This is called as such because the proton or H+ has taken on both lone electron pairs on the oxygen in the water molecule. As such it is s coordinate covalent bond.
Carbon has 6 protons, that's why its atomic number is 6