Question

Chlorophyll a is one of the green pigments found in plants. Chlorophyll a has the molecular formula C55H72MgN4O5. How many atoms are in this molecule?
A)136
B)137
C)138

Answer 1

We add up all the various atoms:
C: 55
H: 72
Mg: 1
N: 4
O: 5

55 + 72 + 1 + 4 + 5
= 137

The answer is B.

Answer 2

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