The isotope notation : 
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Further explanation
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Given
53 protons and 20 neutron
Required
The isotope notation
Solution
Isotopes are elements that have the same atomic number with a different mass number
The following element notation,
X = symbol of element
A = mass number
= number of protons + number of neutrons
Z = atomic number
= number of protons = number of electrons, on neutral elements
So the mass number of element = 5 + 6 11
Atomic number = 5
The symbol :
Phosphorus has 5 valence electrons
A roller coaster reaches its maximum P.E when it is at the top ;)
Chlorine.
If you search Google images for "Aufbau principle periodic table," you'll find some handy diagrams that will make it much easier to determine an element based on its electron configuration. Determine the number of electrons in the last part of the configuration (in this case, 5), locate that group on the Aufbau periodic table diagram, then count that number from left to right within that group. In this case, within the "3p" portion of the Periodic table, count to 5 and you'll find Chlorine as the answer.
Answer: Earth, though the dwarf planet Pluto does have ice on it.
