When long chains of carbon and hydrogen atoms break apart into smaller chains, the temperature decreases. Which type of reaction is this?
A. Combustion
B. Endothermic
C. Replacement
D. Exothermic

With i really need the correct answer!

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

Consider a uniformly charged ring in the xy plane, centered at the origin. the ring has radius a and positive charge qdistributed evenly along its circumference. a)what is the direction of the electric field at any point on the z axis? . b)what is the magnitude of the electric field along the positive z axis? use k in your answer, where k=14πϵ0. d)the ball will oscillate along the z axis between z=d and z=−d in simple harmonic motion. what will be the angular frequency ω of these oscillations? use the approximation d≪a to simplify your calculation; that is, assume that d2+a2≈a2. express your answer in terms of given charges, dimensions, and constants