An organic chemist uses analytical chemistry

Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.

All of the following are homogeneous mixtures except a) sugar dissolved in water. b) orange juice. c) coffee with cream. d) household vinegar. e) apple juice

What is the empirical formula of a compound that is 50.7% antimony and 49.3% selenium ?