Question

How many molecules of carbon dioxide are there in 44.0 grams of the gas? (atomic mass of carbon = 12.0 and atomic mass of oxygen = 16.0)

Answer 1

The answer is 6.023 × 10²³ molecules

Avogadro's number  is the number of units (atoms, molecules) in 1 mole of substance:

6.023 × 10²³ molecules per 1 mole

Let's calculate how many grams are in 1 mole. This is expressed as molar mass Mr:
Mr(CO2) = Ar(C) + 2Ar(O)
Ar(C) = 12
Ar(O) = 16
Mr(CO2) = 12 + 2 * 16 = 12 + 32 = 44 g

There are 44 g in 1 mole.
There are 6.023 × 10²³ molecules in 1 mole.

So there are 44 g in 6.023 × 10²³ molecules