Which statement about fusion reactors is true? a enriched uranium isotopes are used as fuel in fusion reactors. b fuel for fusion reactors can be extracted form ocean water. c fusion reactors are now replacing fission reactors. d fusion reactors produce radioactive waste as spent fuel .

b Fuel for fusion reactors can be extracted from ocean water.  

Explanation:

The fuel is deuterium, which makes up 0.02% of the hydrogen atoms in water. The oceans contain more than a billion cubic kilometres of water, so that's a lot of deuterium.

a is wrong. The fuel for fusion reactors is deuterium.

c is wrong.  There is much research, but there are no large-scale fusion reactors in operation.

d is wrong. Fusion reactors do not produce radioactive waste as spent fuel. Most of the radioactive waste would be the reactor core itself.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6