The atomic number 26 corresponds to iron (Fe). Let's evaluate each statement:
a. There are six electrons in the outermost shell.
Iron has the electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6\). The outermost shell for iron (the fourth shell) has 2 electrons (from 4s) plus 6 electrons (from 3d), totaling 8 electrons. So, this statement is false.
b. The atom has 26 electrons in the nucleus.
Electrons are not found in the nucleus; they orbit around it. The nucleus contains protons and neutrons. An atom with an atomic number of 26 has 26 protons in the nucleus and, in a neutral atom, 26 electrons orbiting around it. Thus, this statement is also false.
c. The outermost energy level is full.
As mentioned, the outermost shell has a total of 8 electrons (2 from 4s and 6 from 3d). The 4s and 3d subshells can hold a total of 18 electrons (2 in the 4s and 10 in the 3d), so the outermost energy level is not full. This statement is false as well.
d. A and b are true.
Since both statements a and b are false, d is false.
Therefore, the correct answer is c.