Blance NH3+Na--->NaNH2+H2

2NH3 + 2Na - > 2NaNH2 + H2

Explanation:

NH3 + Na - > NaNH2 + H2

The above can be balance by doing the following:

There are a total of 4 hydrogen atoms on the right and 3 atoms on the left. This can be balance by putting 2 in front of NH3 and 2 in front of NaNH2 as shown below:

2NH3 + Na - > 2NaNH2 + H2

There are 2 atoms of Na on the right and 1 atom on the left. It can be balance by putting 2 in front of Na as shown below

2NH3 + 2Na - > 2NaNH2 + H2

Now we can see that the equation is balanced as we have equal numbers of atoms of the different elements on both sides of the equation.

2 NH3 + 2 Na = 2 NaNH2 + H2