Answer : The correct options are, litmus paper and phenolphthalein.
Explanation :
Acid : It is a substance that has ability of donating proton or hydrogen ion, \(H^+\).
The properties of an acid are :
Acids are sour in taste.
The texture of an acid solution is sticky.
It changes the color of the litmus paper to red.
Base : It is a substance that has ability of donating hydroxide ion, \(OH^-\).
The properties of an base are :
Base are bitter in taste.
The texture of an base solution is slippery.
It changes the color of the litmus paper to blue.
Indicators : It is a substance that gives the visible sign by the color change of the chemical species like an acid or a base.
Litmus paper : It turns red when it is added to a strong acid, it turns blue or purple when it is added to a strong base and it turns a yellowish-green when it is added to a neutral solution.
Phenolphthalein : It is also used as an indicator in acid–base titrations. It turns colorless in acidic solutions and pink in basic solutions.
Thus, there are two good ways to test whether a solution is an acid or a base which are litmus paper and phenolphthalein.
