Which is a compound? (need explanation please) I need this answer asap (as soon as possible) please

a. Kr

b. O2

c. Cl2

D. CuF2

Why does the sun appear to be the brightest star in the sky? a- its apparent brightness is much greater than other stars. b- it burns more gas, making it brighter than any other star. c- it is the largest star in the galaxy, so it is the brightest star. d- its relative distance to earth is closer than the other stars.

Summarize possible ways in which phases of matter could combine to form a solution.

If blood contains 150g of hemoglobin per liter of blood, how much hemoglobin would be contained in 10 ml of blood