Elements have been discovered with up to energy levels.
a. 5
b. 6
c. 7
d. 8

The best answer I think is 7.  If you look at the periodic table, there are 7 periods and each period has a new energy level.  Because of that, I don't think an element can naturally have more than 7 energy levels, however, it might be possible for an electron in the 7th energy level to briefly go up to an exited state due to energy being added.  

29.1-12=17.1the answer is this one