Final answer:
The stages of a low-mass star's life cycle in order are Protostar, Main Sequence, Red Giant, Planetary Nebula, and White Dwarf. The star loses most of its mass during the Red Giant phase and as it sheds its outer layers to form a Planetary Nebula.
Step-by-step explanation:
For a low-mass star like one with less than 10 solar masses, the correct order of stages in its life cycle from start to finish is: Protostar, Main Sequence, Red Giant, Planetary Nebula, and finally White Dwarf. This sequence corresponds to option 1 in your list. A star begins its life as a contracting Protostar and then spends the majority of its lifetime in the stable Main Sequence phase. As the star exhausts its nuclear fuel, it expands into a Red Giant. Following this stage, the outer layers of the star are expelled creating a Planetary Nebula, exposing the hot inner core. The core then cools and becomes a White Dwarf, which will continue to cool over billions of years.
During the lifetime of a star initially having a mass of 5 Msun that later ends up as a White Dwarf of 0.8 Msun, mass loss occurs primarily during the Red Giant phase and when the star sheds its outer layers to form a Planetary Nebula. These are the stages where the star loses most of its original mass. In the Red Giant phase, strong stellar winds are responsible for the mass loss, while the expulsion of the outer layers forms the Planetary Nebula.