Which gases can be used for storage of fresh sample and of an oil for a long time

Helium and also nitrogen

Explanation:

Helium, as well as nitrogen, can be used for storage of a fresh sample of an oil for a long time because they prevent the oil from rancidity. The contact of air and oil is prevented by using nitrogen or helium as blanketing gas.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-