What is product obtained when B2O3 is reacted with NaOH?
As @Ivan said, it may form metaborate, borax or a tetrahydroxoborate complex all depending on reaction conditions(temperature, pressure, medium, stoichiometry etc.).


$$\ce{B2O3 + 2NaOH -&gt;[\Delta] 2NaBO2 + H2O}$$


Boron trioxide react with sodium hydroxide to produce sodium metaborate and water. This reaction takes place at a temperature of 400-550°C.


$$\ce{2B2O3 + 2NaOH → Na2B4O7 + H2O}$$


Boron trioxide react with sodium hydroxide to produce sodium tetraborate and water. Sodium hydroxide - diluted solution. Boron oxide is amorphous.


$$\ce{B2O3 + 2NaOH + 3H2O → 2Na[B(OH)4]}$$


Boron trioxide react with sodium hydroxide and water to produce sodium tetrahydroxoborate(III). Boron oxide is amorphous. Sodium hydroxide - concentrated solution. The reaction proceeds at room temperature.