Ablock has a volume of 0.07 m3 and a density of 3,500 kg/m3. what's the force of gravity acting on the block (and weight) in the air?
a. 1,715 n b. 686 n c. 2,058 n d. 2,401 n

The force of gravity is simply the mass times the gravitational acceleration, which I suppose is 9.8 m/s^2 in your exercice.
The mass can be obtained from d=m/v, where
d= density,
m=mass
v=volume.
m=3500*0.07=245 kg.
Therefore force of gravity (which is the weight) is F=m*g=245*9.8=2401 N.

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 -