A rat gets light then shock until it responds to the light. Then, it gets light plus tone before shock for additional trials. In later test trials, the rat shows strong reaction to the light and little reaction to the sound. What is this phenomenon called?

Blocking effect

Explanation:

The scenerio described in the question is blocking effect. Blocking effect According to Kamin can be regarded as effect of conditioning of an association that exist between two different stimuli, i.e a conditioned stimulus and unconditioned stimulus which is been impaired if, at the process of conditioning, conditioned stimulus is been presented along with unconditioned stimulus which has been connected along with the unconditioned stimulus. It explained that blocking of conditioning to a stimulus is possible provided that the stimulus is been reinforced in conjunction along with previously conditioned stimulus.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.