Explain why this statement is false: “Because there is no change in composition during a physical change, the appearance of the substance will not change”

The most efficient way to establish the best possible economizer position is to measure

100 grams of molten lead (600°c) is used to make musket balls. if the lead shot is allowed to cool to room temperature (21°c), what is the change in entropy (in j/k) of the lead? (for the specific heat of molten and solid lead use 1.29 j/g⋅°c; the latent heat of fusion and the melting point of lead are 2.45 × 104 j/kg and 327°c, respectively.)

Air can be considered a mixture. which statement does not explain why?