Effort The diagram shows a lever of uniform mass supported at
the middle point. Six coins of equal mass are placed at
mark A on the left hand side.
А
B
(a) Can you balance the lever with 12 more coins of
equal mass? If yes, where would you place them? If
not why?
(b) With six coins still on the left, three coins are put on the right at mark B. Where on
the right should you pile an addition of six coins to get a balance?​

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -

The answer to the question is (a)   

Binary fission and mitosis