Final answer:
Talc is the softest common mineral among the given options
Step-by-step explanation:
The softest common mineral among the given options is talc (c).
Talc has a Mohs hardness scale rating of 1, making it the softest mineral. It can be easily scratched with a fingernail or a copper penny.
Quartz (a), calcite (b), and fluorite (d) are all harder minerals compared to talc. Quartz has a Mohs hardness of 7, followed by calcite with a hardness of 3, and fluorite with a hardness of 4.