calculate the number of K atoms in a 1.00 ug sample of pure KCL. K=39.1 g/mol and KCL= 74.6 g/mol.

How many moles are there in 1 ug KCl?

moles = grams/molar mass
moles KCl = moles K = moles Cl, then
1E-6g/molar mass KCl.
There are 6.022E23 ions K or Cl (or molecules KCl) in 1 mol KCl. Set up a proportion.