Which of the following could result from a substance that undergoes a physical change?
a) its chemical composition is altered.
b) it has an irreversible change.
c) it forms a new substance.
d) its shape is altered.

Its shape is altered.

Explanation:

For example, an ice cube melting into a puddle.

  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-