3. How many atoms are found in 0.000256 moles?

1.54*10^20 atoms

Explanation:

It's done by using the relation

N=n*L where,

N = number of entities present

n = amount of substance (mole)

L = Avogadro's constant which is 6.02*10^23

now from the question, given

n=0.000256

And L=6.02*10^23

N = 0.000256*6.02*10^23

N = 1.54*10^20 atoms