Answer:
Oxygen = 15.999 g/mol
Iron = 3 × 55.845 = 167.535 g/mol
CaCO3 = 20 × 100.0869 = 2001.738 g/mol
The relation between density and mass and volume is

the dose required is 2.5 tsp
each tsp contain 5mL
So dose required in mL = 2.5 X 5 = 12.5 mL
the mass will be calculated using following formula


The mass of dose in grams will be 15.38 g
A, B and D should be the ones you should check