The correct option is A 24%
The formula of calcium nitrate is Ca(NO3)2.
Thus, the formula mass or molecular mass
= Atomic mass of calcium + 2 [(Atomic mass of nitrogen) + ( 3 Atomic mass of oxygen)]
= 40 + 2×[14 + (3×16)]
= 40 + 2×(14 + 48)
= 164
The percentage of calcium would be:
= Mass of calciumMass of calcium nitrate×100 = 40164×100 = 24%