Answer:
2.04×10⁻⁴ moles of Ar
Explanation:
We begin from this knowledge:
1 mol of substance has 6.02×10²³ particles
Let's solve this by a rule of three:
6.02×10²³ atoms are contained in 1 mol of Ar
1.23×10²⁰ atoms must be contained in (1.23×10²⁰ . 1) / 6.02×10²³ =
2.04×10⁻⁴ moles of Ar
