Radioactive decay follows first-order kinetics. The amount of radioactive substance remaining ($N$) after $n$ half-lives is given by the formula:

$N = \frac{N_0}{2^n}$

where $N_0$ is the initial amount of the substance.

Given: Initial amount, $N_0 = 32 \text{ mg}$ Half-life, $t_{1/2} = 12.3 \text{ years}$ Total time, $t = 49.2 \text{ years}$

First, calculate the number of half-lives ($n$): $n = \frac{t}{t_{1/2}} = \frac{49.2 \text{ years}}{12.3 \text{ years}} = 4$

Now, substitute the values into the formula to find the remaining amount: $N = \frac{32}{2^4} = \frac{32}{16} = 2 \text{ mg}$

Therefore, 2 mg of tritium would remain after 49.2 years.