molecular formula is the acutal composition of the components making up the compound
chlorophyll a molecular formula is - C₅₅H₇₂MgN₄O₅
so we have to find how many atoms are in 1 molecule
for this we have to add all the atoms of each element making up this 1 molecule
number of atoms of each element
C - 55
H - 72
Mg - 1
N - 4
O - 5
the sum of all the atoms - 55 + 72 + 1 + 4 + 6 = 138
answer is C ) 138
