Why does the glass seems to disappear in the oil?

When we see glass, we don't see the glass object itself but through other objects in the room are reflected/distorted by the glass. The glass disappeared because both Pyrex and vegetable oil bend (refract) light by the same amount – light travels straight through both materials!

answer: option c. i.e. electric current flowing “downhill” from the negative electrode to the positive electrode in a battery

explanation:

the water analogy to the circuits define the pipes (water flows) to the electric current. now, we know that the electric current flows from the positive terminal to the circuit (as shown in the diagram attached).

hence, option c is the correct answer.

the answer is 3.1 his answer is wrong mines is right