Chemistry question

1.
Carbon-12 is the more abundant of the two stable isotopes of the element carbon, accounting for 98.89% of carbon; it contains 6 protons, 6 neutrons and 6 electrons.
Carbon-12 is of particular importance as it is used as the standard from which atomic masses of all nuclides are measured: its atomic mass is by definition 12.
Prior to 1959 both the IUPAP and IUPAC tended to use oxygen to define the mole, the chemists defining the mole as the number of atoms of oxygen which had mass 16 g, the physicists using a similar definition but with the oxygen-16 isotope only. The two organizations agreed in 1959/1960 to define the mole as:
' The mole is the amount of substance of a system which contains as many elementary
entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol." '
This was adopted by the CIPM (International Committee for Weights and Measures) in 1967, and in 1971 it was adopted by the 14th CGPM (General Conference on Weights and Measures).
In 1980 the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their ground state.

2.
The Aufbau (building up) Principle:
a. the number of electrons in an atom is equal to the atomic number;
b. each added electron will enter the orbitals in the order of increasing energy;
c. an orbital cannot take more than 2 electrons.

圖片參考：http://www.avogadro.co.uk/light/aufbau/levels.gif


3.
Electrolysis of water is an electrolytic process which decomposes water into oxygen and hydrogen gas with the aid of an electric current, where a power source such as a 6 volt battery is commonly used. The electrolysis cell consists of two electrodes (usually an inert metal such as platinum) submerged in an electrolyte and connected to opposite poles of a source of direct current.
Hoffman voltameter used to electrolyze water.

圖片參考：http://content.answers.com/main/content/wp/en/4/4c/Hoffman_voltameter.jpg

I hope this can help with your understanding. =)