What were the first 16 elements known in 1760

The discovery of the first basic elements in nature was sufficient to begin the era of industrial revolution through combining two or more of these elements in order to speed up the production processes.

The first discovered elements in nature were:
sulphur
chlorine
argon
neon
carbon
oxygen
helium
silicon
calcium
hydrogen
nitrogen 
sodium
fluorine
lithium
aluminum

This is a simple matter of looking up the discovery date of the elements.  And the results are Known since ancient times Copper, Sulfur, Silver, Tin, Antimony, Gold, Mercury, Lead Then somewhere around 1400, Bismuth. 1669 Phosphorus 1694 Carbon 1735 Iron 1735 Platinum 1751 Nickel, Cobalt 1755 Magnesium The list in alphabetical order is: Antimony, Bismuth, Carbon, Cobalt, Copper, Gold, Iron, Lead, Magnesium, Mercury, Nickel, Phosphorus, Platinum, Silver, Sulfur, and Tin

Answer earth,water,fire and air;

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.