Given:
Percentage composition of C: 39.9%
Percentage composition of H: 6.7%
Molecular weight of the compound: 180

To find: Number of carbon atoms present in the molecule.

Let's assume the number of carbon atoms in the molecule is x.

1. Calculation of the number of carbon atoms:
The percentage composition of carbon (C) in the compound is given as 39.9%. This means that the compound contains 39.9 grams of carbon for every 100 grams of the compound.

To calculate the number of carbon atoms, we need to convert the percentage into grams. The molar mass of carbon (C) is 12 g/mol.

The number of moles of carbon (C) in the compound can be calculated using the formula:
moles = (mass of element / molar mass of element)

Therefore, the number of moles of carbon (C) can be calculated as:
moles of carbon (C) = (39.9 g / 12 g/mol) = 3.325 mol

Since 1 mol of carbon (C) contains Avogadro's number (6.022 x 10^23) of atoms, the number of carbon atoms (x) can be calculated as:
x = (3.325 mol) x (6.022 x 10^23 atoms/mol) = 2.00 x 10^24 atoms

2. Calculation of the number of hydrogen atoms:
The percentage composition of hydrogen (H) in the compound is given as 6.7%. This means that the compound contains 6.7 grams of hydrogen for every 100 grams of the compound.

To calculate the number of hydrogen atoms, we need to convert the percentage into grams. The molar mass of hydrogen (H) is 1 g/mol.

The number of moles of hydrogen (H) in the compound can be calculated using the formula:
moles = (mass of element / molar mass of element)

Therefore, the number of moles of hydrogen (H) can be calculated as:
moles of hydrogen (H) = (6.7 g / 1 g/mol) = 6.7 mol

Since 1 mol of hydrogen (H) contains Avogadro's number (6.022 x 10^23) of atoms, the number of hydrogen atoms can be calculated as:
Number of hydrogen atoms = (6.7 mol) x (6.022 x 10^23 atoms/mol) = 4.03 x 10^24 atoms

3. Calculation of the number of oxygen atoms:
The total percentage composition of all elements in a compound is equal to 100%. Therefore, the percentage composition of oxygen (O) can be calculated as:
Percentage of oxygen (O) = 100% - (Percentage of carbon (C) + Percentage of hydrogen (H))
Percentage of oxygen (O) = 100% - (39.9% + 6.7%) = 53.4%

Since the molecular weight of the compound is 180 g/mol, the mass of oxygen (O) in the compound can be calculated as:
mass of oxygen (O) = (Percentage of oxygen (O) / 100) x Molecular weight of the compound
mass of oxygen (O) = (53.4 / 100) x 180 g = 96.12 g

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