Which of the following is an appropriate unit to measure large distances across the universe? an astronomical unit a kilometer a light year a mile

A light year

Explanation:

Yeah, if you're measuring across the universe, a light year is the only really appropriate unit of measurement you could be using. Given the vast amount of distance that light would cover in a year, one light year is extremely large.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.