To calculate the number of carbon atoms in 84.3 g of ethyne, we need to divide the given mass by the molar mass of ethyne and then multiply by the number of carbon atoms per molecule of ethyne:

1. Calculate the number of moles of ethyne:

Moles of ethyne = Mass / Molar mass

Moles of ethyne = 84.3 g / 26.04 g/mol (molar mass of C2H2)

Moles of ethyne = 3.24 mol

2. Multiply the number of moles by the number of carbon atoms per molecule:

Each molecule of ethyne (C2H2) contains 2 carbon atoms.

Number of carbon atoms = Moles of ethyne × Number of carbon atoms per molecule

Number of carbon atoms = 3.24 mol × 2

Number of carbon atoms = 6.48 mol

Therefore, 84.3 g of ethyne contains approximately 6.48 mol of carbon atoms.