Why must a chemical equation be balanced?

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

Which metal exist in liquid state and can be cut with knife ?

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?