If an adult dog has 78 chromosomes, the number of chromosomes in a dog’s sperm cell will be

39

Explanation:

Well with humans, each parent has half of the chromosomes that the baby will have, the sperm has half and the egg has the other set. So, I assume that if the puppy doesn't end up with any extra or less chromosome, it will get half of them from the sperm.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.