Opposite pairs form ionic bonds, due to this the answer is D - Li and Br; They have unlike charges.
I'm pretty sure it's Nuclear Reactions. Not very sure.
Answer:
Boron has a larger radius and the protons in carbon exert more pull.
Explanation:
Remember than elements have greater radius as they are closer to the bottom left corner, so boron would have the larger radius here. Carbon has a smaller radius, which makes it easier for the protons in carbon to exert more pull.
When 2.50 g is burned then in oxygen then 1.25kj of heat is produced.