When aluminum reacts with sodium hydroxide (NaOH), it produces hydrogen gas (H2). The chemical reaction between aluminum and sodium hydroxide can be represented as follows:

2Al(s) + 6NaOH(aq) + 6H2O(l) → 3Na2Al(OH)6(aq) + 3H2(g)

In this reaction, aluminum metal (Al) reacts with sodium hydroxide (NaOH) and water (H2O) to form sodium aluminate (Na2Al(OH)6), which is a water-soluble compound, and hydrogen gas (H2). Hydrogen gas is released as a byproduct of the reaction and can be observed as bubbles forming on the surface of the reaction mixture.