One of the foci for the moon's orbit would be the
(1) sun (3) mars
(2) earth (4) venus

The question is oversimplified, and pretty sloppy.

Relative to the Earth . . .
The Moon is in an elliptical orbit around us, with a period of
27.32... days, and with the Earth at one focus of the ellipse.

Relative to the Sun . . .
The Moon is in an elliptical orbit around the Sun, with a period
of 365.24... days, and with the Sun at one focus of the ellipse,
and the Moon itself makes little dimples or squiggles in its orbit
on account of the gravitational influence of the nearby Earth.

I'm sorry if that seems complicated.  You know that motion is
always relative to something, and the solar system is not simple.

Protons have a positive charge and, collectively, give an element its atomic number.