A radioactive element has decay constant $\lambda$ (expressed in $\mathrm{s}^{-1}$). The number of nuclei of this element at $t=0$ is $N$. What is the expected number of nuclei that will have decayed after 1 s ?

A radioactive element has decay constant $\lambda$ (expressed in $\mathrm{s}^{-1}$). The number of nuclei of this element at $t=0$ is $N$. What is the expected number of nuclei that will have decayed after 1 s ?