Answer
a) Tellurium
b) Rubidium
c) Argon
d) Astatine
Work Step by Step
a) Oxygen lies in group (family) 16.
In group 16, lies Tellurium, whose most stable ion is $Te^{2-}$.
Tellurium has atomic number = 52, and thus number of protons = 52.
Since the ion has a 2- charge on it, number of electrons will be two more than the number of protons.
Thus number of electrons of $Te^{2-}$ = 54 + 2 = 54.
b) The alkali metal family has the element rubidium (Rb), whose most stable ion is $Rb^{+}$.
Its atomic number = 37 , which means it has 37 protons, and 37 electrons. BUT, in its ion form, it loses one electron to form the $Rb^{+}$ ion. Thus number of electrons of $Rb^{+}$ = 36.
c) 18 protons mean that the atomic number of that noble gas is 18.
Noble gas of atomic number 18 is Argon ( Refer to periodic table )
d) 85 protons mean that the atomic number of that halogen is 85.
Halogen of atomic number 85 is Astatine Refer to periodic table )
