a. The symbol [tex]\tt _{11}^{23}Na[/tex], [tex]\tt _{18}^{40}Ar[/tex], [tex]\tt _{15}^{31}P^{3-}[/tex], [tex]\tt _{13}^{27}Al^{3+}[/tex]
b. Isotope of Na
Further explanation
Atomic number=number of protons=number of electrons(neutral atom)
Number of neutrons=mass number-atomic number
Mass number=protons+neutrons
B. atomic number=11, mass number=11+12=23⇒Sodium
[tex]\tt _{11}^{23}Na[/tex]
C. atomic number=18, mass number=18+22=40⇒Argon
[tex]\tt _{18}^{40}Ar[/tex]
D. atomic number=15, mass number=15+16=31, charge -3(electron-proton)⇒Phosphor
[tex]\tt _{15}^{31}P^{3-}[/tex]
E. atomic number=13, mass number=13+14=27, charge +3(proton-electron)⇒Aluminium
[tex]\tt _{13}^{27}Al^{3+}[/tex]
Isotope=the same atomic mass, different neutron(mass number)
So the atom⇒isotope of Sodium(Na)
