Can someone help me with number 4? Please and thank you

Which real-world scenarios below represent physical and chemical changes? -running a car -exploding fireworks -mixing water and powdered drink mix -combining oil and vinegar to make salad dressing -taking aspirin for a headache -diluting bleach with water-digesting dinner-spreading peanut butter on bread

Light waves can move through , but they travel fastest when they move through a(n) .

How many moles of bromine are needed to produce 3.23 moles of potassium bromide