What is one example of a scientific model? (this is science I don't know why can't find it on "pick a subject" so yeah)

What does x represent in the formula for the compound xcl4?

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

Joan writes four numbers on the board in standard form, and then she writes their scientific notation