__NH3(g) + __ O2(g) → __ N2(g) + __ H2O(g)

When the reaction above is completely balanced, the coefficient for NH3 will be

(a)
2.
(b)
3.
(c)
4.
(d)
6.

I get

4 NH3 + 3 O2--> 2 N2 + 6 H2O

To balance the equation:

__NH3(g) + __O2(g) → __N2(g) + __H2O(g)

We need to count the number of atoms for each element on both sides of the equation.

On the left side:
- We have 1 N atom from NH3.
- We have 3 H atoms from NH3.

On the right side:
- We have 2 N atoms from N2.
- We have 2 H atoms from H2O.

Now, let's balance the nitrogen (N) atoms. Since we have 1 N atom on the left side and 2 N atoms on the right side, we need to multiply the NH3 by 2 to balance the N atoms:

2 NH3(g) + __O2(g) → 2 N2(g) + __H2O(g)

Next, let's balance the hydrogen (H) atoms. Since we have 3 H atoms on the left side and 2 H atoms on the right side, we need to multiply the H2O by 3/2 to balance the H atoms:

2 NH3(g) + __O2(g) → 2 N2(g) + 3/2 H2O(g)

Now, we can see that the coefficient for NH3 is 2.

Therefore, the correct answer is (a) 2.

To balance the chemical equation NH3(g) + O2(g) → N2(g) + H2O(g), you need to adjust the coefficients in front of each compound so that the number of atoms of each element is the same on both sides of the equation.

To balance the nitrogen (N) atoms, you must have the same number on both sides of the equation. In this case, there is only one nitrogen atom in NH3 and one in N2. Therefore, the coefficient for NH3 must be 1.

Thus, the correct answer is (a) 1.