The best way to determine the number of atoms of arsenic in the sample will be to multiply 2.3 by Avagadro's number.
This is because Avagadro's number is the number of particles one mole of any substance has, and its value is 6.02 x 10²³
If the number of moles of a substance are known, then multiplying by Avagadro's number will give the number of particles. In this case, this is 1.38 x 10²⁴.
Periodic table is an arrangement of chemical elements in an organized manner with atomic number. Elements are distributed in columns and groups in periodic table according to their properties.
Many elements have their isotopes and mostly are radioactive but isotopes are not mentioned on the periodic table, elements are mentioned there and all trans-uranium elements are most radioactive.