Question 2 (1 point) Which of the following does NOT involve a chemical reaction?
Fallen leaves decay in a compost pile.
Leaves change color in the fall.
O A fire burns a pile of fallen leaves.
A pond freezes over in the winter.

D. A pond freezing over is not a chemical reaction, it is a physical reaction.

  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-