1. Red dwarfs (stellar mass M ∈[0.075 M_☉, 0.5 M_☉]) have a convection zone that extends over their whole interior if they have less than about 0.35 M_☉ (see Wikipedia: Red dwarf: Description and characteristics).

    They are fully convective because their relatively low temperaturature gives them a relatively high opacity to electromagnetic radiation (EMR). This favors convection over radiative transfer.

    The red dwarfs have uniform composition because of the mixing of convection and eventually will convert a large fraction of their hydrogen to helium before they end their nuclear burning lives (see Wikipedia: Red dwarf: Description and characteristics)---but this has never happened to any of them yet because their main-sequence lifetimes are greater than age of the observable universe since the Big Bang 13.75(11) Gyr (see Wikipedia: Concordance model: Parameters)

  2. Intermediate-mass stars (e.g., the Sun) have interior radiative zone and a surface convection zone. The surface composition of these stars does NOT evolve while they are on the main sequence.

    The convection zone shrinks as mass increases above 1 M_☉ and disappears at ∼ 1.2 M_☉ (see Wikipedia: Radiative zone: Main-sequence stars). Stars of this mass transport energy only by radiative transfer

  3. Above ∼ 1.3 M_☉, the CNO cycle for hydrogen burning produces most of the input energy rather than the proton-proton chain reaction which dominates at lower masses (see Wikipedia: Convection zone: Main-sequence stars).

    Because the CNO cycle has a stronger temperature dependence than the proton-proton chain reaction, the energy input for stars > 1.3 M_☉ rises more steeply toward the center than in the stars < 1.3 M_☉, and a core convection zone occurs.

    In some very massive stars, the convection zone may reach to the surface: i.e., the stellar photosphere (see Wikipedia: Convection zone: Main-sequence stars).