Litmus paper is used to detect the presence of an acid or a base. Red litmus paper turns blue when a base is detected, and blue litmus paper turns red when acid is detected. In this example, litmus paper is acting as an A. Indicator
B. Chemical Reaction
C. characteristic
D. Benedict's test

A: Indicator

Explanation:

An indicator is a substance that reacts when exposed to other acidic or alkaline substances, which is exactly what litmus paper does, so litmus paper is acting as an indicator.

Indicator

Explanation:

because it indicate about the solution is it basic or acidic.

hope it helps

what's the

  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-