What is a metal replacement reaction

Two things that biomedical has invented or innvated

Fill in the coefficients that will balance the following reaction: a0cr2(so4)3 + a1agno3

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