= Solution
Four mechanisms are \b[<Jeans escape>, <hydrodynamic escape>, <Roche-lobe overflow> and <nonthermal atmospheric escape>].
<Jeans escape> is loss from the high-speed tail of a nearly <Maxwell-Boltzmann velocity distribution> near the exobase. It is sensitive to the escape parameter $\lambda_J=GM_p\mu m_H/(k_BT_{\rm exo}R_{\rm exo})$ and favors light species in a hot, weakly bound atmosphere.
<Hydrodynamic escape> occurs when strong XUV heating drives a bulk outflow, which can entrain heavier species. An illustrative energy-limited scale is $\dot M\sim\eta\pi R_p^3F_{\rm XUV}/(GM_pK_{\rm tide})$ when the absorption and planet radii are comparable; efficiency, radiative losses and recombination can invalidate that simple limit.
<Roche-lobe overflow> removes gas through the low effective-potential barrier toward the inner Lagrange point when the extended atmosphere approaches the <Roche lobe>. Tides can also assist a wind before actual overflow.
<Nonthermal atmospheric escape> includes ion pickup, sputtering, charge exchange and energetic photochemical products. Stellar-wind interactions and photoionization supply particles with escape energies not represented by the local thermal tail. These mechanisms can act together rather than constituting four mutually exclusive evolutionary states.
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