Which of the following is a mixture

a. ice cube

b. candy bar

c. sugar

d. cotton ball

B.) Candy Bar because contains multiple ingredients.

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I think the answer is D.a cotton ball as cotton balls are made up of  fibres of 2 different materials :polyester, and cotton

all the other options are compounds

  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-