Balance the following reaction. A coefficient of "1" is understood. Choose option "blank" for the correct answer if the
coefficient is "1"
___NH₂ + __O₂ ___N2 + ___H₂O

2NH₂ + O₂ → N₂ + 2H₂O

Explanation:

Balancing the equation means, the number of atoms on both sides of the equation must be the same.

In the case of the given equation, we have to find out whether it is balanced or not.

2NH₂ + O₂ →  N₂ + 2H₂O

Atoms       Number of atoms before balancing     after balancing

                 LHS                 RHS                                    LHS         RHS

N               1                        2                                            2              2

H               2                       2                                            4              4                        

O               2                       1                                            2                2

To balance the N atoms, we have to put 2 in front of NH₂, and then to balance the H, O atoms, we have to put 2 in front of H₂O, so that each atom in left hand as well as right hand side of the equation was balanced.