Questions

When combining with nonmetallic atoms, metallic atoms generally will Lose electrons and forms cations.

As the ionization energy of te metals are very low, so they can easily lose electrons and form positively charged ion called cations.

Let that something be 'x'

From the given data,

x + x/5 = 21

5x + x/5 = 21

6x = 21 x 5

=> x = 17.5

Hence, that something is x = 17.5.

One fathom = 1.8288 meters = 6 feet

A fathom is a unit of length used especially for measuring the depth of water.

Eukaryotic cells all have a nucleus. Eukaryotes are organisms that are multicellular, although there are some examples of single cellular eukaryotes. So eukaryotic cells can be either cell with a nucleus or a eukaryotic organism's cell.

The most important feature to judge whether it has nucleus membrane.

And for other choices, they are the common features of eukaryote and prokaryote.