1mole of Cl atoms contain the Avogadro's number 6x10 exp 23(10 to the power of 23)
there for xmoles of Cl atoms is contained in 1.72x1022atoms
xmoles =1.72x1022 divided by 6x10exp 23
2.93 exp -23moles(2.93 x10 to the power of -23)
Hope It helped Let me know if did!!!!