Which of these is an example of a solution?
a. hot cocoa
b. water
c. nacl
d. sugar

Hot cocoa.

Explanation:

A solution may be defined as the substances that contain a solute and solvent. The substance which is to be dissolved is solute and the substance in which it is dissolved is solvent.

Hot cocoa consist of cocoa as solute with sugar. The milk is used as ab solvent in the hot cocoa. Hence, the hot cocoa acts as the solution with some solute and solvent.

Thus, the answer is option (A).

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.