I'd say d.) Concentrated in the nucleus.
This is because Nucleus consists of protons and neutrons; contributing to some mass, whereas Electron's mass is almost negligible ( 9.1 x 10^-31 kg)
Hope this answers your question!
Answer:

Explanation:
For an electromagnetic wave, the relationship between magnetic field amplitude and electric field amplitude is given by

where
E is the amplitude of the electric field
c is the speed of light
B is the amplitude of the magnetic field
For the electromagnetic wave in this problem, we have
E = 10 V/m is the amplitude of the electric field
So if we solve the formula for B, we find the amplitude of the magnetic field:

The era after the KT event occurred
When all atoms that make up a substance are the same, then that substance is an element. Elements are made of only one kind of atom. Because of this, elements are called "pure"