General electronic configuration of outermost and penultimate shell of an atom is (n-1)s^{2} (n-1)p^{6} (n -1)d^{x} ns^{2} . If n=4 the number of proton in the nucleus is
Substituting the values, we get the configuration to be
The atomic number is 10+2+6+2+5=25
Number of proton = Atomic number
Therefore, the number of protons in the nucleus is 25.