Which one of the following metal oxides does not usually react with sodium hydroxide?

Metal oxides are generally basic in nature [2]. Basic oxides react with acids to form salt and water but do not typically react with other bases like sodium hydroxide (NaOH). Copper oxide (CuO) is a basic oxide and does not react with NaOH. In contrast, aluminium oxide (Al2O3) is amphoteric, meaning it reacts with both acids and bases [2]; it reacts with NaOH to form sodium aluminate. Potassium oxide (K2O) and calcium oxide (CaO) are strongly basic oxides that react vigorously with water to form their respective hydroxides, potassium hydroxide and calcium hydroxide [3]. While K2O and CaO are highly reactive with water, they do not undergo a neutralization-type reaction with NaOH because they are all basic species. However, among the options, copper oxide is the standard example of a basic oxide that remains inert toward strong alkalis like NaOH under normal conditions.

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.9 > p. 41
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.10 > p. 43
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Figure 1.3 > p. 6