Sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)$_2$] are strong bases commonly used in laboratories and industries. Zinc oxide (ZnO) is an amphoteric oxide, meaning it can behave both as a base and as an acid. Sodium sulphate (Na$_2$SO$_4$) is a neutral salt formed by the reaction of a strong acid (sulphuric acid) and a strong base (sodium hydroxide). It does not exhibit basic properties. Therefore, the correct answer is Sodium sulphate.