Hydrogen (H).
it’s atomic number is 1, so it’s the first element in the periodic table.
https://en.wikipedia.org/wiki/File:Simple_Periodic_Table_Chart-en.svg
it burns to give H20, i.e. water.
it is filled in zeppelins, as it is light weight gas.

how about a Merman.

CO2 i.e. Carbon Dioxide
since, the carbonated drinks and dry ice have it.

273.727273 revolutions

Let the red filled circle represent 1
the other one represent 0
binary decimal
001 – 1
010 – 2
100 – 4
011 – 3

the sellsword will kill for money, rich man got it. Rich man lives.

24 times

let the boy with hole in his cake have it all, but the other has give something to his brother and he will be let with this 

one can also go other ways around the lines.

she has 36 chalks. she uses 1 chalk each day.
(5/6 + 1/6)+(4/6 + 2/6 )+ …….(36 times)  =   1+1+…1   =    36 .