Awater molecule is made up of one oxygen and teo hydrogen atoms. why is water considered a pure substance

To protect all four receptacles on a branch circuit that surrounds a swimming pool, you would install which of the following configurations? a. gfci feed-through receptacle at the end of the load's circuit b. gfci-terminated receptacle at the beginning of the load's circuit c. gfci feed-through receptacle at the beginning of the load's circuit and the other receptacles connected to the load side of that receptacle d. gfci-terminated receptacle at each end of the load's circuit

The free body diagram shows a box being pulled to the left up a 25-degree incline. the magnitude of the normal force is

What are similarities and differences of reflection, refraction, diffraction and absorption?