Answer: C.) polyatomic anion
Explanation: Cations are the ions which carry a positive charge and anions are the ions which carry a negative charge. Monoatomic ions are those which consists atoms of similar elements and polyatomic ions are those which consists of atoms of different elements.
For example : 
is a monoatomic cation.
is an monoatomic anion.
is a polyatomic cation.
is a polyatomic anion as it consists of atoms of phosphorous and oxygen and bears a negative charge.
Answer:
electromagnetic wave
Explanation:
Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate.
The compound is Molecular
Answer:
(b) gas and dust
Explanation:
"The interstellar medium is the stuff between the stars. Made up mostly of hydrogen and helium gas – plus trace amounts of ices, silicate grains, and all the other elements – it contains all the material needed to make stars and planets. It is shaped by stellar winds, dying stars, galactic magnetic fields, and supernova explosions."
"The interstellar medium is filled primarily with hydrogen gas. A relatively significant amount of helium has also been detected, along with smaller percentages of such substances as calcium, sodium, water, ammonia, and formaldehyde . Sizable quantities of dust particles of uncertain composition are present as well."
