Taking into account the definition of avogadro's number, 1.95×10²⁴ atoms are present in 84.3 g of ethyne.
Avogadro's Number is called the number of particles that make up a substance (usually atoms or molecules) and that can be found in the amount of one mole of said substance. Its value is 6.023×10²³ particles per mole. Avogadro's number applies to any substance.
So, first of all you need to know how many moles of ethyne 84.3 g contains. Since the molar mass of C₂H₂ is 26 g / mole (that is, the more that one mole of the substance contains), the following rule of three can be applied: if 26 g are contained in 1 mole, 84.3 g are contained in how many moles of the compound?
[tex]amount of moles=\frac{84.3 gx1 mole}{26 g}[/tex]
amount of moles= 3.24 moles
Now you can apply the following rule of three: if 1 mole of ethyne contains 6.023×10²³ atoms, then 3.24 moles of the compound how many atoms does it contain?
[tex]amount of atoms=\frac{3.24 molesx6.023x10^{23} atoms}{1 mole}[/tex]
amount of atoms= 1.95×10²⁴ atoms
Finally, 1.95×10²⁴ atoms are present in 84.3 g of ethyne.
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