The correct answer is it becomes warm.Concept:Acid:Acids are chemical species that donate protons or release H+ ions when dissolved in water.They change the colour of the blue litmus solution to red.Base:Bases are chemical species that release OH‚¬€œ ions when dissolved in water. Sodium hydroxide is a strong base and has a pH value greater than 7.They change the colour of the red litmus solution to blue.Explanation:The reaction between an acid and a base is known as neutralisation reaction, and when an acid neutralises the effect of an acid and a base, salt (sodium chloride) and water are formed, as well as energy in the form of heat is evolved.HCl+NaOH ? NaCl + H2ONeutralisation is an exothermic reaction (heat is evolved) which result in the formation of salt.Water (H+ and OH- react to form H2O) is produced by neutralisation reactions between the acidic proton from the acid and the hydroxyl group of the base. When a few drops of NaOH are added to a test tube containing HCl, the test tube becomes warm because of the neutralization effect.