4. Greta passed a comb through her hair several times. She then placed the comb next to a stream of water flowing from a faucet. Greta observed the stream of water bend toward the comb. How did passing a comb through her hair allow the comb to bend the stream of water?
A) by making the comb more absorbent
B) by giving the comb an electrical charge
C) by increasing the thermal energy of the comb
D) by breaking some of the chemical bonds in the comb

the correct answer is B

  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-