Which of the following statements is true?
u-235 is an isotope of uranium.
hydrogen atoms are heavier than uranium atoms.
fusion reactions require extremely low temperatures.
chemical energy is the energy inside the nucleus of an atom.

U-235 is a isotope of Uranium

Explanation:

We know, Uranium is naturally occurring element that has radioactive nature and has no stable isotope. Uranium is made up of 3 major isotopes Which are U-238 found in 99.27–99.27% natural abundance, U-235 found in 0.72% and U-234 found in 0.0051% abundance.

The list of isotopes is Uranium-233, Uranium-234 and Uranium-235. Hence, U-235 is a isotope of Uranium is the correct statement.

why is arctic sea ice important? arctic sea ice keeps the polar regions cool and moderate global climate. sea ice has a bright surface; 80 percent of the sunlight that strikes it is reflected back into space. as sea ice melts in the summer, it exposes the dark ocean surface.