#### Answer

(a) $N_2 + 3H_2 -- \gt 2NH_3$
(b) 450. $N_2$ molecules.
(c) 300. $NH_3$ molecules.

#### Work Step by Step

(a) Balance the equation:
$N_2 + H_2 -- \gt NH_3$
- Balance $N$:
The coefficient for nitrogen on the reactants is "2" from $N_2$, so we should put that number as the coefficient of $NH_3$:
$N_2 + H_2 -- \gt 2NH_3$
- Balance $H$:
There is a total of 6 hydrogens on the products, so we should put a "$\frac{6}{2}$" (which is 3) as the coefficient of $H_2$;
$N_2 + 3H_2 -- \gt 2NH_3$
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Use the coefficients as conversion factors:
(b) According to the balanced equation, the ratio of nitrogen molecules to hydrogen molecules is 1:3, so:
150. $N_2$ $\times \frac{3H_2}{1N_2} = 450. H_2$
(c) According to the balanced equation, the ratio of nitrogen molecules to ammonia is 1:2, so:
150. $N_2$ $\times \frac{2NH_3}{1N_2} = 300. NH_3$