The base has a bitter taste and a slippery texture. A base dissolved in water is called an alkali. When chemically reacting with acids such compounds produce salts. Bases are known to turn blue on red litmus paper.
When a base reacts with a metal, hydrogen gas is produced. It burns with a pop sound when a burning candle is brought near the mouth of the test tube.
Metal + Base → Hydrogen + Salt
Sodium hydroxide as it reacts with zinc metal gives hydrogen gas & sodium zincate.
2 NaOH + Zn → H2 + Na2ZnO2