Well, it's really dangerous to try and visualize physical models for things
of this size. But if you must, then it's something like this:
-- The nucleus is a tight-packed bunch of protons and neutrons, located
at the center of each atom.
-- The electrons live all around the nucleus, in a space far from it.
A description of the relative sizes that I read more than 60 years ago
and always stuck with me goes like this: The nucleus in the middle
and the electrons whizzing around it have a size-relationship that's
about the same as a bunch of grapes in the middle of the state of Texas.
This also tells us that matter is mostly empty space !
-- In Bohr's model of the atom, he described the whole thing very much
like a miniature solar system ... the electrons are tiny, solid little balls,
orbiting the nucleus like planets around the sun.
We learned later that it's impossible to talk about things like "how big is
the electron" or "where is the electron" or "how much momentum does
the electron have". The best we can do is talk about a 'cloud' around the
nucleus ... it has some mass and some negative charge, and portions
of it somehow exist at different levels of energy, and can jump to
different levels.
This is NOT because we don't have good enough technology yet to
zoom in on the electrons, and at some time in the future we'll be able
to sharply see where they are and how fast they're moving. It's because
on the scale of atomic dimensions, there is NO SUCH THING as "where
is it" or "how big is it" or "how fast is it moving". These don't exist.
"Location" is described in terms of probability, objects behave like solid
waves, and an object can have this much energy or that much energy
but NO AMOUNT OF ENERGY IN BETWEEN.
Weird ? Hard to understand ? You said it !
BTW ... the answer to the question is ' A ' .
