The uncertainty principle is
$\Delta E \times \Delta t \ge {h \over {4\pi }}$
Half filled and fully filled orbitals have greater stability due to greater exchange energy, greater symmetry and more balanced arrangement.
The energy of 2s-orbital is less than the energy of 2p-orbital in case of hydrogen like atoms.
de-Broglie's wavelength is given by
$\lambda = {h \over {mv}}$, where m = mass of the particle,
v $=$ group velocity of the particle.
