What does it mean when the question is asking which element is present and how many atoms each element has ?

In which layer of earth do most earthauakes occur a_ inner core b_outer core c_mantle d_crust

Ascientist measures the speed of sound in a monatomic gas to be 449 m/s at 20∘c. what is the molar mass of this gas?

Suppose you mix one mole of sulfuric acid (h2so4) with 1 mole of sodium hydroxide(naoh). why does the ph of the solution remain below 7? ( explain so i can get better understanding! )