13.toluene + nbs/light, followed by nbs /light (repeat reaction a total of 3 times), then hno3/h2so4 a. 3-no2(ph)cbr b. 4-no2(ph)cbr c. 4-nitrotoluene d. 4-nitro-1,3,5-tribromobenzene e. a-d incorrect

  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-

the objects have the same charge is correct.

nathan lee