Here we need to determine the number of radio nodes that exist for a 5F orbital. Remember the number of radio nodes is equal to N-L+1. Since the number of the orbital is five, that tells us it's in the 5th shell of an atom, so N=5.

Since the letter is F, that tells us what L is. Remember when the letter is F, our sub level letter, that means that L=3, so that L=3+1. So this comes out to 5-4, which means that there's only one radio node for a 5F orbital.