How does an acid–base indicator react when placed in an acidic solution?

it changes color.
it dissolves.
it increases the ph of the solution.
it releases hydroxide ions.

Option (a) is the correct answer.

Explanation:

An acid-base indicator is an indicator which changes color according to the pH of solution in which it is placed.

For example, phenolphthalein is an acid-base indicator.

Thus, we can conclude that out of the given options, an acid–base indicator react by changing color when placed in an acidic solution, is the correct option.

  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-