It gives visible feedback based on whether the substance being checked is an acid or an alkali
        
             
        
        
        
Answer:
mostly gasoline in cars nowadays
 
        
                    
             
        
        
        
A. water
the word hydro means water
        
             
        
        
        
Answer:
Exothermic reaction: In exothermic reaction, energy is transferred to the surroundings, and the surrounding temperature increases, this is known as exothermic reaction. In other words energy exits in exothermic reaction. Some example of exothermic reactions are:
1) Neutralisation reaction.
2) Combustion reaction.
3) Some oxidation reaction.
Endothermic reaction: In endothermic reaction, energy is taken in from the surrounding, and the surrounding temperature decreases, this is known as endothermic reaction. In other words energy enters in endothermic reaction. Some example of exothermic reactions are:
1) Thermal decomposition.
2) Reaction between citric acid and sodium hydrogen carbonate.