This question is about the properties and behavior of radioactive decay in a laboratory.

Which of the following statements is/are true?

1. The activity of a sample is independent of its temperature, physical state, and chemical composition.
2. For two radioactive samples with the same initial activity, the sample with the larger decay constant will have a greater initial number of undecayed nuclei.
3. A plot of the natural logarithm of activity, $\ln (A)$, against time, $t$, yields a straight line with a gradient equal to $-\lambda$, where $\lambda$ is the decay constant of the isotope.