Why alkali metal impart characteristic colours when introduced to flame

Iknow #2 is d. i just need to know why

Read these sentences from the text. near the equator, the tropics receive the most rain on a consistent basis. as a result, the fresh water falling into the ocean decrease the salinity of the surface water in that region. [. .] . . as the salt content of sea water increases, so does its density. what can you infer about how rain affects the density of surface water near the equator?

Asample of aluminum foil contains 8.60 × 1023 atoms. what is the mass of the foil?