The element with an atomic mass of $16$ is oxygen (O). Its diatomic molecule is $\text{O}_2$, which contains a total of $16$ electrons. According to the Molecular Orbital Theory, the electronic configuration of the $\text{O}_2$ molecule is: $\sigma 1s^2, \sigma^* 1s^2, \sigma 2s^2, \sigma^* 2s^2, \sigma 2p_z^2, (\pi 2p_x^2 = \pi 2p_y^2), (\pi^* 2p_x^1 = \pi^* 2p_y^1)$ As seen from the configuration, there are $2$ unpaired electrons present in the degenerate $\pi^* 2p_x$ and $\pi^* 2p_y$ antibonding molecular orbitals. This presence of unpaired electrons is responsible for the paramagnetic nature of the oxygen molecule.