Answer:
c) 4f1
Step-by-step explanation:
Based on Aufbau principle electrons in an atom or ion fill up such that the orbital of the lowest energy gets occupied first followed by those with higher energy. The energy ordering of atomic orbitals is therefore:
1s>2s>2p>3s>3p>4s>3d>4p>5s>4d>5p>6s>4f.....
The integers 1,2,3 .. represent the principal quantum number 'n'
s,p,d,f are the atomic orbitals each of which can accommodate a maximum of 2, 6, 10 and 14 electrons respectively.
As per the energy ordering, the 4f orbital is highest in energy and hence the single electron present in the 4f orbital represented by the configuration 4f1 will have the highest energy.