The half-life for a 400-gram sample of radioactive element X is 3 days. How much of element X remains after 15 days have passed? A.
12.5 g

B.
25 g

C.
50 g

D.
100 g

Which of these best describes an ionic bond?

This image is an example of a(n) a) atom. b) compound. c) mixture. d) molecule.

Nitric acid can be formed in two steps from the atmospheric gases nitrogen and oxygen, plus hydrogen prepared by reforming natural gas. in the first step, nitrogen and hydrogen react to form ammonia: (g) (g) (g) in the second step, ammonia and oxygen react to form nitric acid and water: (g) (g) (g) (g) calculate the net change in enthalpy for the formation of one mole of nitric acid from nitrogen, hydrogen and oxygen from these reactions. round your answer to the nearest .