At is the chemical symbol of astatine.
At is a radioactive halogen that is itself the byproduct of the decay of more massive radioactive atoms. It has a very short half life, and the "world supply" of astatine (the amount believed to exist at any particular moment anywhere in the entire mass of the planet) is about one ounce (approx. 30 grams).
11 is the atomic number for the element sodium in the periodic table.
Calcium.
cerium
iron
water
N stands for Nitrogen on the periodic table.
Beryilium
iodine
there is no such element
iodine
Argon is what Ar stands for on the Periodic Table of elements.
Sr stands for strontium on the periodic table of elements.
11 is the atomic number for the element sodium in the periodic table.
potassium
Beryllium (Be)
it is fluorine
Calcium.