Endothermic reaction is the reaction in which the system absorbs energy. The system absorbs heat and cools the surroundings. Reactants are the substances that are involved in the reaction and at the end of the reaction product are formed.
In the endothermic reaction because heat is absorbed , the products have a higher heat.
Answer : The number of moles of oxygen needed are, 1.5 moles.
Explanation :
The balanced chemical reaction will be:

Now we have to calculate the moles of oxygen.
From the balanced chemical reaction we conclude that,
As, 6 moles of water vapor produces from 5 moles of oxygen
So, 1.80 moles of water vapor produces from
moles of oxygen
Therefore, the number of moles of oxygen needed are, 1.5 moles.
It has covelent bonds at 180 degrees between H & N