What clues did you observe when testing the known solids that denote chemical reactivity?

what was your solid and what test you performed on it?
pl give me full information

SOLID: MgO, NaHCO3, CaCO3, unknown.
Conditions: solid alone before adding any liquid, solid with distilled water, solid with acid, solid and acid with universal indicator

what was your observations of the unknown solid?

Solid water: grainy white
Solid w/ distilled water: doesnt dissolve
solid w/ acid: bubble
Solid and acid: nothing

Pl send me your observations
these questions are related to lab performed by you
How can I predict observations ?

only CaCO3 is fitted in this observation.It is insoluble in water and forms bubbles of CO2

so the unknown compound is CaCO3 ?

yes it appears to be CaCO3 from the information provided by you