For the function \( f(x) = a(b)^x \) to be a model for exponential decay, the value of \( b \) must meet certain conditions. Specifically, for exponential decay, we need \( 0 < b < 1 \).
Thus, the correct statement that best describes the conditions for \( f(x) \) to be a model for exponential decay is:
\( 0 < b < 1 \).