Endothermic Reaction:

An endothermic reaction is a chemical reaction that absorbs heat energy from its surroundings. In other words, the products of an endothermic reaction have more energy than the reactants, and energy is taken in from the surroundings to facilitate the reaction.

Among the given options, the endothermic reaction can be identified as follows:

Option a) 2H2 + O2 = 2H2O

This reaction represents the combustion of hydrogen gas (H2) with oxygen gas (O2) to form water (H2O). This is an exothermic reaction because it releases heat energy. The formation of water is accompanied by the release of energy, making it an exothermic process.

Option b) N2 + O2 = 2NO

This is also an exothermic reaction. It represents the formation of nitrogen monoxide (NO) from nitrogen gas (N2) and oxygen gas (O2). The reaction releases heat energy as the products have lower energy than the reactants.

Option c) 2NaOH + H2SO4 = Na2SO4 + 2H2O

The reaction above involves the combination of sodium hydroxide (NaOH) with sulfuric acid (H2SO4) to produce sodium sulfate (Na2SO4) and water (H2O). This is an exothermic reaction as it releases heat energy during the process.

Option d) 3O2 + C2H5OH = 2CO2 + 3H2O

This reaction represents the combustion of ethanol (C2H5OH) with oxygen gas (O2) to form carbon dioxide (CO2) and water (H2O). This is an exothermic reaction because it releases heat energy.

Conclusion:

Among the given options, there is no endothermic reaction. All the provided reactions are exothermic as they release heat energy during the process.

I think option B is right becz dissociation energy of N2 molecule is very high, As in normal cases N2 molecules in our atmosphere don't combine with O2, it combines at the time of lightening.