The number of atoms in 1 dm3 of aluminum is nearly the same as the number of atoms in 1 dm3 of lead, but the densities of these metals are very different (see table 1.5). explain

Difference in atomic mass of Al and Pb makes their densities different

Explanation:

We know that

Here volume of both Al and Pb are

Again they have similar number of atoms in volume

But atomic mass of Al is 27 amu and atomic mass of Pb is 207 amu.

Mass of an element in volume would be summation of atomic masses of all atoms present.

As difference in atomic masses between Al and Pb is quite high therefore it is expected that their densities would be very different.

3 hours because it is a decent distance.