Not by any practical or economic means. In principle you could distill brass to separate copper and zinc by boiling point but this obviously poses significant technical challenges. The more realistic way is through hydrometallurgy, where the brass is dissolved in an aqueous solution and the two component metals separated by chemical or electrochemical means. This includes selective leaching of zinc from brass, which should be possible although I have not looked up any specific references for this. In practice the energy required is too great and it is far easier to just remelt scrap brass to make new brass.

There are two main astrophysical processes that produce heavy nuclides, the s-process and the r-process. Both involve neutron capture onto stable nuclides followed by beta decay, but they differ greatly in terms of timescale. The s-process (s for slow) occurs in environments where there is a low but stable neutron flux, such that nuclei have a good chance of decaying before they capture another neutron. The r-process (r for rapid), on the other hand, happens when the neutron flux is so high that beta decay is slow compared to neutron capture. Consequently, nuclei get stuffed with as many neutrons as they can physically hold, until they undergo beta decay and can accept more neutrons.

The s-process is limited to the heaviest stable element, lead, because further neutron captures eventually produce polonium, the most stable isotope of which has a half-life of just over 125 years. Nuclei typically go several thousand years between neutron captures, so the s-process runs into a wall at polonium. The r-process generally produces the heaviest elements including the transuranics, and also the most neutron-rich isotopes of lighter post-iron elements.

The s-process occurs mostly in dying stars, where nuclei can hang around for a relatively long time in the stellar envelope before being lost through stellar winds, or shed as planetary nebulae. The r-process was originally thought to occur in core-collapse supernovae (ccSNe) but modelling suggests that it is unlikely to account for more than a small fraction of the r-process nuclides we observe. Instead, binary neutron star mergers are now the leading candidate for hosting the r-process.

Water has a hydrogen atom number density of 111 mol/L, while that of liquid hydrogen is 70.3 mol/L. No, it's not just due to water having a higher molecular weight.

Neutron stars, like other astronomical bodies made of degenerate matter, shrink in radius as their mass increases.