Which definitions of acids can apply to substances?

*Acids taste sour. The lemon, vinegar, tamarind contain acids; that's why they are sour.

*The acids change the color of certain substances called indicators. The indicators have the property of changing color as the character acid or basic solutions. The litmus and phenolphthalein are indicators of acids and bases. The solution of phenolphthalein is colorless red in the presence of an acid. Already the blue litmus paper turns red.

*The acids react with bases to form salts and water. This reaction is called neutralization reaction.
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