Question

10 grams of caco3 contains 0.15 moles of oxygen reasom

Answer 1

That is because of the ration of its mass in CaCO3. You can use the following calculations to prove this:
Find ratio using relative atomic mass of the constituting elements.
Ca= 40
C=  12
O=16
mass of CaCO3= 40+12+(16x3)=  100

mass of Oxygen in CaCO3= 48 ---- 48/100 x 10
                                                   =4.8g

mass of oxygen in the calcium carbonate= 4.8 g. Calculate the moles
Moles = mass/ molar mass    mass=4.8
                                 molar mass of oxygen= 16x2=32  

moles=    4.8/32
       =  0.15 moles  (the moles of oxygen in CaCO3)

Answer 2

Here,,,,

Ca = 40

C = 12

O = 16

Mass of CaCO3 = 40+12+(16×3) = 100

Mass of oxygen in CaCO3 = 48

= 48/100 × 10

= 4.8g

Mass of oxygen is 4.8g

Now,,we will calculate the moles :-

Moles = Mass

Molar mass

Mass = 4.8

Molar mass = 16×2 = 32

so,,, Moles = 4.8 = 0.15

32

Therefore,,,, 0.15 moles of oxygen in 10 gram of CaCO3....