The aluminium metal reacts with sodium hydroxide to produce sodium aluminate and hydrogen gas.

The reaction is as follows:

$2\mathrm{Al}\left(\mathrm{s}\right) + 2\mathrm{NaOH}\left(\mathrm{aq}\right) + 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \to 2{\mathrm{NaAlO}}_2\left(\mathrm{aq}\right) + 3{\mathrm{H}}_2\left(\mathrm{g}\right)$

It can be tested by bringing a burning candle near the reaction. A continuous burning with a pop sound is observed.