No. 1a. Atom 1 must be sodium (Na)
No. 1b. Atom 2 must me calcium (Ca)
No. 2 Isotopes are elements with theSAME NUMBER OF PROTONS but with DIFFERENT NUMBERS OF NEUTRON. The number of neutrons can be determined by SUBTRACTING the atomic number from the ATOMIC MASS. The mass number is THE TOTAL NUMBER OF PROTONS AND NEUTRONS.
3. The number of protons