The correct option is the first one:

The function that typically models the decay of a substance over time is an exponential decay function.
The correct expression for modeling the mass of a substance in grams after decaying for
years is typically given by the exponential decay formula:
![\[ R(t) = R_0 \cdot e^(-kt) \]](https://img.qammunity.org/2024/formulas/mathematics/high-school/lxmua6123y7j95ntvfomamqup8aqbyopcb.png)
Here:
-
is the mass of the substance at time
,
-
is the initial mass of the substance,
-
is the mathematical constant approximately equal to 2.71828,
-
is the decay constant.
The correct choice from the options you provided is:
![\[ R(t) = (100)^t \]](https://img.qammunity.org/2024/formulas/mathematics/high-school/kjnuszfi3cejihil7fwy6nej5yfl60ffrj.png)
This is an exponential function where the base is less than 1 (in this case,
), indicating decay.
The exponent t represents the time in years, and R(t) gives the mass of the substance at time t. The base raised to the power of t ensures that the mass decreases over time.
So, the correct option is the first one:
.